Mohammad was especially moved by the cordial welcome extended to his fellow-countrymen by his new disciples. But, with his great insight concerning the souls of mortals, he resolved to tighten the bonds of such touching friendship. So that it should be proof against all insinuations dictated by the rivalry, inevitable in the future, between the Muhajirun who had forsaken their country, families and wealth to follow him; and the Ansars who had offered the safe shelter and material assistance to which his triumph was due. Would not each party have some little reason to claim for it alone first rank in the Prophet's affection and the annals of Islam?
In order to avoid such dangerous contingencies and create real family ties for the exiles, Mohammad profited by the cloudless exaltation uniting Muhajirun and Ansars just then, to issue a decree of perfect brotherhood between them. He ordained that they should pair off in couples consisting of a man of the Mohajirun and an Ansar. 'Fraternise in Allah!' he told them. 'Ye are brothers!' Henceforward, every Mussulman of Al-Madinah had for brother a Mussulman of Makkah.
It would be sheer madness to try and find words to express the degree of devotion attained by this brotherhood of religion, stronger than ties of blood, for it was supernatural. All these men's hearts, united in the love of Allah, were now nothing more than a single heart, palpitating in different breasts. Each man loved his brother better than himself, and during the first years of the Hegira, when one died, the other inherited his property, to the exclusion of his natural heirs.
Among the fraternal unions thus constituted, we may note those of Abu Bakr with Kharijah ibn Zayd; Ummar with Usman ibn Malik; Abu Ubaidah with Sad ibn Muaz; and Usman ibn Affan with Aus ibn Najar. The prophet had been the first to choose Ali for his brother, thus sealing the bond of fraternity that he had signed when beginning his mission. But as Ali belonged to the Muhajirun, the Ansars might have been vexed because the Apostle did not choose a brother in their ranks. That was why, at the death of one of their Najibs, Asad ibn Zararah, Mohammad took his place as Najib, pretexting that he was one of them, because his uncle on his mother's side had formerly dwelt in their city.