After the murder of ʿUthman ﵁ in Dhu al-Hijja 35 AH, Medina was in shock. Aisha ﵂ was returning from the hajj to Mecca and heard the news on the way. There in Mecca she joined Talha ﵁ and Zubayr ﵁, two of the ten who had been promised Paradise. Three voices, three figures of authority from the first generation of Islam, demanded one thing: that the murderers of ʿUthman ﵁ be called to account.
ʿAli ﵁ had accepted the bayʿah in Medina, with hesitation. He knew that the murderers were among his own supporters, and that an immediate hunt for them would plunge the caliphate into civil war before it was established. He asked for time. Mecca accepted no delay. In Jumada al-Akhira 36 AH a coalition of roughly three thousand men set out, with Aisha ﵂ in her armored howdah on a great red camel that would later give the battle its name.
The coalition chose Basra as its objective. Basra had a large Quraysh population, sympathy for the cause of ʿUthman ﵁, and a governor (ʿUthman ibn Hunayf ﵁) appointed by ʿAli ﵁ but without a sizable garrison. On the way, at the watering place of al-Hawʾab, Aisha ﵂ heard dogs barking. She cried out that the Prophet ﷺ had warned her of this place. Men from the coalition hurried forward with witnesses who swore that this was not al-Hawʾab. She rode on.
Basra was occupied after skirmishes with ʿUthman ibn Hunayf ﵁. ʿAli ﵁ gathered his followers in Medina and marched via Rabadha and al-Kufa, where Ammar ﵁ and Hasan ﵁ brought thousands under the banner. At the end of Jumada he came within striking distance of Basra. The two armies camped within sight of each other.