Sunnan Abu Dawud Collection: ::Book Number 14:: Hadith # 2518
Narrated Ubaydullah ibn Khalid as-Sulami: The Apostle of Allah (peace_be_upon_him) made a brotherhood between two men, one of whom was killed (in Allah's path), and a week or thereabouts later the other died, and we prayed at his funeral). The Apostle of Allah (peace_be_upon_him) asked: What did you say? We replied: We prayed for him and said: O Allah, forgive him, and join him to his companion. The Apostle of Allah (peace_be_upon_him) said: What about his prayers since the time the other died, and his fasting since the time the other died--the narrator Shu'bah doubted the words, "his fasting--and his deeds since the time the other died. The distance between them is just like the distance between heaven and earth.