Musnad Ahmad 1163:17

Yahya ibn Sa'id narrated to us, from Abu Bakkar, who said: I prayed behind Abu al-Malih over a funeral, and he said: "Straighten your rows, and let your intercession be sincere. If I were to choose a man, I would have chosen him." Then he said: Abdullah ibn Sulayt narrated to me. [Abdullah said:] My father said: And Abu Ubaydah al-Haddad narrated to us, saying: Abdullah ibn Sulayt narrated to me, from one of the wives of the Prophet, peace and blessings of Allah be upon him, Maymunah—and he was her foster brother—that the Messenger of Allah, peace and blessings of Allah be upon him, said: "There is no Muslim upon whom a community (ummah) prays, except that they intercede for him." And Abu al-Malih said: "The community (ummah) is forty to one hundred, and more."