It is narrated from Ubayd bin Khalid (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) established brotherhood between two men. One of them was martyred in the way of Allah, and then the other died about a week later. When the companions (may Allah be pleased with them) offered his funeral prayer, the Prophet (peace and blessings of Allah be upon him) said: "What supplication did you make for him?" They replied, "We prayed to Allah to forgive him, have mercy on him, and unite him with his companion." The Prophet (peace and blessings of Allah be upon him) said: "Where did the prayers go that he offered after his companion's prayers? And where did the deeds go that he performed after him?" Or he said: "Where did the fasts go that he observed after him?" The distance between the two is greater than the distance between the earth and the sky." Hasan, narrated by Abu Dawood and Nasa'i.