Sa‘d b. Abu Waqqas and Abu Bakra reported God’s Messenger as saying, "If anyone knowingly claims as father one who is not his father, paradise is forbidden to him.”
Narrated Abu Huraira told that he heard the Prophet say when the verse about invoking curses1 came down:
"Any woman who brings into a family one who does not belong to it can expect no mercy from God (or is no observer of God’s religion) and God will not bring her into His paradise; and God will veil Himself from any man who disowns his child when he looks at him, and shame him in the presence of all creatures, first and last.”
One day God's Messenger visited me looking pleased and asked if I was not surprised to hear that Mujazziz al-Mudlijl1 had entered, and seeing Usama and Zaid2 with a rug over them covering their heads and letting their feet appear, said, “These feet are related.”
(Bukhari and Muslim.)
1. Members of the tribe of Mudlij were said to have a reputation for being able to trace relationship from physical features.
2. Usama was Zaid's son.