Khalid ibn al-Walid
According to the modern historian Meir Jacob Kister, it was likely the threat posed by this army which compelled Musaylima to forge an alliance with Sajah. Ikrima was repelled by Musaylima's forces and thereafter instructed by Abu Bakr to quell rebellions in Oman and Mahra (central southern Arabia) while Shurahbil was to remain in the Yamama in expectation of Khalid's large army.
After his victories against the Bedouin of Najd, Khalid headed to the Yamama with warnings of the Hanifa's military prowess and instructions by Abu Bakr to act severely toward the tribe should he be victorious. The 12th-century historian Ibn Hubaysh al-Asadi holds that the armies of Khalid and Musaylima respectively stood at 4,500 and 4,000. Kister dismisses the much larger figures cited by most of the early Muslim sources as exaggerations. Khalid's first three assaults against Musaylima at the plain of Aqraba were beaten back. The strength of Musaylima's warriors, the superiority of their swords and the fickleness of the Bedouin contingents in Khalid's ranks were all reasons cited by the Muslims for their initial failures. Khalid heeded the counsel of the Ansarite Thabit ibn Qays to exclude the Bedouins from the next fight.
In the fourth assault against the Hanifa, the Muhajirun under Khalid and the Ansar under Thabit killed a lieutenant of Musaylima, who subsequently fled with part of his army. The Muslims pursued the Hanifa to a large enclosed garden which Musaylima used to stage a last stand against the Muslims. The enclosure was stormed by the Muslims, Musaylima was slain and most of the Hanifites were killed or wounded. The enclosure became known as the 'garden of death' for the high casualties suffered by both sides.
Khalid assigned a Hanifite taken captive early in the campaign, Mujja'a ibn al-Murara, to assess the strength, morale and intentions of the Hanifa in their Yamama fortresses in the aftermath of Musaylima's slaying. Mujja'a had the women and children of the tribe dress and pose as men at the openings of the forts in a ruse to boost their leverage with Khalid; he relayed to Khalid that the Hanifa still counted numerous warriors determined to continue the fight against the Muslims. This assessment, along with the exhaustion of his own troops, compelled Khalid to accept Mujja'a's counsel for a ceasefire with the Hanifa, despite Abu Bakr's directives to pursue retreating Hanifites and execute Hanifite prisoners of war.
Khalid's terms with the Hanifa entailed the tribe's conversion to Islam and the surrender of their arms and armor and stockpiles of gold and silver. Abu Bakr ratified the treaty, though he remained opposed to Khalid's concessions and warned that the Hanifa would remain eternally faithful to Musaylima. The treaty was further consecrated by Khalid's marriage to Mujja'a's daughter. According to Lecker, Mujja'a's ruse may have been invented by the Islamic tradition "in order to protect Khalid's policy because the negotiated treaty ... caused the Muslims great losses". Khalid was allotted an orchard and a field in each village included in the treaty with the Hanifa, while the villages excluded from the treaty were subject to punitive measures. Among these villages were Musaylima's hometown al-Haddar and Mar'at, whose inhabitants were expelled or enslaved and the villages resettled with tribesmen from clans of the Tamim.

Conclusion of the Ridda wars: The traditional sources place the final suppression of the Arab tribes of the Ridda wars before March 633, though Caetani insists the campaigns must have continued into 634. The tribes in Bahrayn may have resisted the Muslims until the middle of 634. A number of the early Islamic sources ascribe a role for Khalid on the Bahrayn front after his victory over the Hanifa. Shoufani deems this improbable, while allowing the possibility that Khalid had earlier sent detachments from his army to reinforce the main Muslim commander in Bahrayn, al-Ala al-Hadhrami.
The Muslim war efforts, in which Khalid played a vital part, secured Medina's dominance over the strong tribes of Arabia, which sought to diminish Islamic authority in the peninsula, and restored the nascent Muslim state's prestige. According to Lecker, Khalid and the other Qurayshite generals "gained precious experience [during the Ridda wars] in mobilizing large multi-tribal armies over long distances" and "benefited from the close acquaintance of the Kuraysh [sic] with tribal politics throughout Arabia".

Campaigns in Iraq: With the Yamama pacified, Khalid marched northward toward Sasanian territory in Iraq (lower Mesopotamia). He reorganized his army, possibly because the bulk of the Muhajirun may have withdrawn to Medina. According to the historian Khalil Athamina, the remnants of Khalid's army consisted of nomadic Arabs from Medina's environs whose chiefs were appointed to replace the vacant command posts left by the sahaba ('companions' of Muhammad). The historian Fred Donner holds that the Muhajirun and the Ansar still formed the core of his army, along with a large proportion of nomadic Arabs likely from the Muzayna, Tayy, Tamim, Asad and Ghatafan tribes. The commanders of the tribal contingents appointed by Khalid were Adi ibn Hatim of the Tayy and Asim ibn Amr of the Tamim. He arrived at the southern Iraqi frontier with about 1,000 warriors in the late spring or early summer of 633.
The focus of Khalid's offensive was the western banks of the Euphrates river and the nomadic Arabs who dwelt there. The details of the campaign's itinerary are inconsistent in the early Muslim sources, though Donner asserts that "the general course of Khalid's progress in the first part of his campaigning in Iraq can be quite clearly traced". The 9th-century histories of al-Baladhuri and Khalifa ibn Khayyat hold Khalid's first major battle in Iraq was his victory over the Sasanian garrison at Ubulla (the ancient Apologos, near modern Basra) and the nearby village of Khurayba, though al-Tabari (d. 923) considers attribution of the victory to Khalid as erroneous and that Ubulla was conquered later by Utba ibn Ghazwan al-Mazini. Donner accepts the town's conquest by Utba "somewhat later than 634" is the more likely scenario, though the historian Khalid Yahya Blankinship argues "Khālid at least may have led a raid there although [Utbah] actually reduced the area".
From Ubulla's vicinity, Khalid marched up the western bank of the Euphrates where he clashed with the small Sasanian garrisons who guarded the Iraqi frontier from nomadic incursions. The clashes occurred at Dhat al-Salasil, Nahr al-Mar'a (a canal connecting the Euphrates with the Tigris immediately north of Ubulla), Madhar (a town several days north of Ubulla), Ullays (likely the ancient trade center of Vologesias) and Walaja. The last two places were in the vicinity of al-Hira, a predominantly Arab market town and the Sasanian administrative center for the middle Euphrates valley.
Al-Hira's capture was the most significant gain of Khalid's campaign. After besting the city's Persian cavalry under the commander Azadhbih in minor clashes, Khalid and part of his army entered the unwalled city. Al-Hira's Arab tribal nobles, many of whom were Nestorian Christians with blood ties to the nomadic tribes on the city's western desert fringes, barricaded in their scattered fortified palaces. In the meantime, the other part of Khalid's army harried the villages in al-Hira's orbit, many of which were captured or capitulated on tributary terms with the Muslims. The Arab nobility of al-Hira surrendered in an agreement with Khalid whereby the city paid a tribute in return for assurances that al-Hira's churches and palaces would not be disturbed. The annual sum to be paid by al-Hira amounted to 60,000 or 90,000 silver dirhams, which Khalid forwarded to Medina, marking the first tribute the Caliphate received from Iraq.
During the engagements in and around al-Hira, Khalid received key assistance from al-Muthanna ibn Haritha and his Shayban tribe, who had been raiding this frontier for a considerable period before Khalid's arrival, though it is not clear if al-Muthanna's earlier activities were linked to the nascent Muslim state. After Khalid departed, he left al-Muthanna in practical control of al-Hira and its vicinity. He received similar assistance from the Sadus clan of the Dhuhl tribe under Qutba ibn Qatada and the Ijl tribe under al-Madh'ur ibn Adi during the engagements at Ubulla and Walaja.