What justifications did the Muhajirun and Ansar rely upon to assert their right to the Caliphate?

The Companions hastened to choose a caliph after the death of the Prophet (peace be upon him) out of concern for Islam. The Ansar gathered in Saqifah Bani Sa'idah, believing they had a greater right to the caliphate, while the Muhajirun believed they had a greater right because the Arabs would not unite except under a man from Quraysh. When the strength of the Muhajirun's argument became clear to the Ansar, they submitted to them and pledged allegiance to Abu Bakr Al-Siddiq.