Musnad Ahmad 574:3

'Affan narrated to us, Shu'bah narrated to us, Ibn Murrah narrated to us, he said: I heard 'Amr ibn Maymun, from 'Abdullah ibn Rabi'ah, from 'Ubayd ibn Khalid, a man from Banu Sulaym, who said: The Messenger of Allah (peace and blessings of Allah be upon him) established brotherhood between two men. One of them was killed, and the other died after him, so we prayed over him. The Messenger of Allah (peace and blessings of Allah be upon him) said: "What did you say?" They said: We prayed for him that He may forgive him, and have mercy on him, and join him with his companion. The Messenger of Allah (peace and blessings of Allah be upon him) said: "Then where is his prayer after his prayer, and his deed after his deed, or his fasting after his fasting?" He said: "Indeed, what is between them is like what is between the heaven and the earth."