Musnad Ahmad 574:1

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, 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 (may Allah bless him and grant him peace) 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 (may Allah bless him and grant him peace) said: "What did you say?" They replied: "We supplicated for him: 'O Allah, join him with his companion.'" The Messenger of Allah (may Allah bless him and grant him peace) said: "Where is his prayer after his prayer? And where is his fasting after his fasting? And where is his deed after his deed?"—Shu‘bah was in doubt regarding the prayer and the deed, [unsure] which of the two it was—"The [difference] between them is like the distance between the heaven and the earth."