Anyone falsely claims to be the son of other than his father, knowing that he is not his father, will be forbidden to enter Paradise
Authentic hadithعن سعد بن أبي وقاص رضي الله عنه مرفوعاً: «من ادعى إلى غير أبيه -وهو يعلم أنه غير أبيه-، فالجنة عليه حرام».
Sa‘d ibn Abi Waqqās (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "Anyone falsely claims to be the son of other than his father, knowing that he is not his father, will be forbidden to enter Paradise."
Explanation
This Hadīth warns against one of the practices done by people in the pre-Islamic era. It was attributing oneself to other than one's real father. Man has to be attributed to one's real family, i.e. the father, the grandfather, up to all levels. It is not permissible for the Muslim to attribute oneself to other than his father, knowing that such a man is not one's real father. For example, if one's father belongs to a certain tribe that has some inferiority, and he thus claims to belong to a superior tribe, this person is forbidden to enter Paradise.
Source · Narrated by Bukhari & Muslim
From the Hadith Encyclopedia (hadeethenc.com).