Musannaf Ibn Abi Shayba 33:200

Ghundar narrated to us, from Shu'bah, from 'Amr ibn Murrah, from 'Amr ibn Maymun, from 'Abdullah ibn Rabi'ah, from 'Ubayd ibn Khalid al-Sulami, who said: The Messenger of Allah (peace and blessings of Allah be upon him) established a bond of 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 replied: "We supplicated to Allah for him: 'O Allah, 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 fasting after his fasting, and where is his deed after his deed? For the difference between them is like the distance between the heaven and the earth." (He expressed doubt regarding the fasting and the deed).