Musannaf Ibn Abi Shaybah

Hazrat Mansur, may Allah have mercy on him, narrates that Hazrat Mujahid, may Allah have mercy on him, said: The first seven people to openly declare Islam were: the Messenger of Allah, peace and blessings be upon him, Hazrat Abu Bakr, may Allah be pleased with him, Hazrat Bilal, may Allah be pleased with him, Hazrat Khabbab, may Allah be pleased with him, Hazrat Suhaib, may Allah be pleased with him, Hazrat Ammar, may Allah be pleased with him, and Hazrat Sumayyah, may Allah be pleased with her, who was the mother of Hazrat Ammar, may Allah be pleased with him. In any case, the Messenger of Allah, peace and blessings be upon him, was protected by his uncle, and Abu Bakr, may Allah be pleased with him, was protected by his people, but the rest were seized, and then the disbelievers made them wear iron armor and placed them in the heat of the sun. Until one of them had to endure extreme hardships, so they gave them whatever they asked for. Members of each man's tribe would bring water in a large leather bag and put them in it, then lift them up by their sides, except for Hazrat Bilal, may Allah be pleased with him. The disbelievers put a rope around his neck and ordered the children to drag him between the two mountains of Mecca. Even in that state, he, may Allah be pleased with him, would say: "Ahad, Ahad" (Allah is One, Allah is One).