Corps commander Ikrimah ibn Abi-Jahl is instructed to make contact with Musaylima at Yamamah, but not to engage in fighting until Khalid joins him.
Abu Bakr's intention in giving Ikrimah this mission is to tie Musaylima down at Yamamah.
With Ikrimah on the horizon, Musaylima will remain in expectation of a Muslim attack, and thus not be able to leave his base.
With Musaylima so committed, Khalid will be free to deal with the apostate tribes of north-central Arabia without interference from Yamamah.
Meanwhile Abu Bakr sends Shurhabil's corps to reinforce Ikrama at Yamamah.
Ikrimah, however, in early September 632 attacks Musaylima's forces and is defeated.
He writes the details of his actions to Abu Bakr, who, both pained and angered by the rashness of Ikrimah and his disobedience, orders him to proceed with his force to Oman to assist Hudayfah; once Hudayfah has completed his task, to march to Mahra to help Arfaja, and thereafter go to Yemen to help Muhajir.
Meanwhile Abu Bakr sends orders to Khalid to march against Musaylima.
Shurhabil's corps, which is stationed at Yamamah, is to reinforce Khalid's corps.
In addition to this, Abu Bakr assembles a fresh army of Ansar and Muhajireen in Medina that joins Khalid's corps at Butah.
From Butah, Khalid marches to Yamamah to join with Shurhabil's corps.
Though Abu Bakr had instructed Shurhabil not to engage Musaylima's forces until the arrival of Khalid, shortly before the arrival of Khalid, Shurhabil engages Musaylima's forces and is defeated too.
Khalid joins with the corps of Shurhabil early in December 632.
The combined force of Muslims, now thirteen thousand strong, defeats Musaylima's army in the Battle of Yamama, which is fought in the third week of December 632 CE.
The fortified city of Yamamah surrenders peacefully later that week.
Khalid establishes his headquarters at Yamamah, from where he dispatches columns to all over the plain of Aqraba to subdue the region around Yamamah and to kill or capture all who resist.
Hereafter, all of central Arabia submits to Medina.
What remains of the apostasy in the less vital areas of Arabia will be rooted out by the Muslims in a series of well planned campaigns within five months.
