What is the ruling on publicly lying by an individual's affiliation with a tribe other than his original tribe for the purpose of boasting, and what are the legal proofs for that?

We advise you to be keen on guiding your people and teaching them, while seeking help through supplication and gentleness. It is not permissible for a person to change their lineage. Whoever claims a father other than his own, while knowing he is not his father, Paradise is forbidden to him. It is reported in the Hadith: "There is no man who claims a father other than his own, knowing it, except that he has committed disbelief. And whoever claims kinship with a people to whom he has no relation, let him take his seat in the Fire." And also: "Whoever claims a father other than his own, or affiliates himself with other than his masters, upon him is the curse of Allah, the angels, and all people. Allah will not accept from him on the Day of Resurrection any repentance or ransom." The disbelief mentioned in the Hadith has two interpretations: either it is for one who deems it permissible, or it is a disbelief in blessings, kindness, the right of Allah Almighty, and the right of his father. The preponderant view is that it is a disbelief in blessings, in the sense of severe warning and deterrence.