stylistic:tone
March to Syria

All early Islamic accounts agree that Khalid was ordered by Abu Bakr to leave Iraq for Syria to support Muslim forces already present there. Most of these accounts hold that the caliph's order was prompted by requests for reinforcements by the Muslim commanders in Syria. Khalid likely began his march to Syria in early April 634. He left small Muslim garrisons in the conquered cities of Iraq under the overall military command of al-Muthanna ibn Haritha.

The chronological sequence of events after Khalid's operations in Ayn al-Tamr is inconsistent and confused. According to Donner, Khalid undertook two further principal operations before embarking on his march to Syria, which have often been conflated by the sources with events that occurred during the march. One of the operations was against Dumat al-Jandal and the other against the Namir and Taghlib tribes present along the western banks of the upper Euphrates valley as far as the Balikh tributary and the Jabal al-Bishri mountains northeast of Palmyra. It is unclear which engagement occurred first, though both were Muslim efforts to bring the mostly nomadic Arab tribes of north Arabia and the Syrian steppe under Medina's control.

In the Dumat al-Jandal campaign, Khalid was instructed by Abu Bakr or requested by one of the commanders of the campaign, al-Walid ibn Uqba, to reinforce the lead commander Iyad ibn Ghanm 's faltering siege of the oasis town. Its defenders were backed by their nomadic allies from the Byzantine-confederate tribes, the Ghassanids, Tanukhids, Salihids, Bahra and Banu Kalb. Khalid left Ayn al-Tamr for Dumat al-Jandal where the combined Muslim forces bested the defenders in a pitched battle. Afterward, Khalid executed the town's Kindite leader Ukaydir, who had defected from Medina following Muhammad's death, while the Kalbite chief Wadi'a was spared after the intercession of his Tamimite allies in the Muslims' camp.

The historians Michael Jan de Goeje and Caetani dismiss altogether that Khalid led an expedition to Dumat al-Jandal following his Iraqi campaign and that the city mentioned in the traditional sources was likely the town by the same name near al-Hira. The historian Laura Veccia Vaglieri calls their assessment "logical" and writes that "it seems impossible that Khālid could have made such a detour which would have taken him so far out of his way while delaying the accomplishment of his mission ". Vaglieri surmises that the oasis was conquered by Iyad ibn Ghanm or possibly Amr ibn al-As as the latter had been previously tasked during the Ridda wars with suppressing Wadi'a, who had barricaded himself in Dumat al-Jandal. Crone, dismissing Khalid's role in Iraq entirely, asserts that Khalid had definitively captured Dumat al-Jandal in the 631 campaign and from there crossed the desert to engage in the Syrian conquest.