Musnad Ahmad 273:1

Abu al-Nadr narrated to us, he said: Shu'bah narrated to us, from 'Amr ibn Murrah, he said: I heard 'Amr ibn Maymun narrating from 'Abdullah ibn Rabi'ah al-Sulami, from 'Ubayd ibn Khalid al-Sulami, and he was one of the companions of the Prophet, may God bless him and grant him peace, he said: The Prophet, may God bless him and grant him peace, established brotherhood between two men. One of them was killed during the time of the Prophet, may God bless him and grant him peace. Then the other died, so they prayed over him. The Prophet, may God bless him and grant him peace, said: "What did you say?" They said: "We said: O God, forgive him; O God, have mercy on him; O God, join him with his companion." The Prophet, may God bless him and grant him peace, said: "Where is his prayer after his prayer? And where is his fasting or his deed after his deed? The distance between them is as the distance between the heaven and the earth."