Ubayy ibn Ka‘b (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "When Adam died, the angels washed his body with water an odd number of times, dug him a grave, and said: 'This is the tradition for Adam's children.'"
When Adam (peace be upon him) died, the angels washed his body with water an odd number of times, which could be one, three, or five times, and dug a hole in the side of the grave and buried him therein. Then they said: "This is the tradition for Adam's children." In other words, the children of Adam should go through the same procedure of washing and burial that their father went through. Indeed, only the guided among Adam's children will abide by this tradition.