There is nothing wrong with having celebrations on the occasions of marriage or other worldly occasions provided that they are free of reprehensible matters such as free mixing and music. Among the impermissible celebrations in Islam are those in which there is any imitation of the disbelievers such as birthday celebrations and Mother’s Day.

Seeking barakah from this hair is not permissible and it is a means that may lead to shirk, because it is impossible to prove that it is actually a hair of the Prophet (blessings and peace of Allah be upon him). By the same token, it is not permissible to build a mosque for it and keep it in that mosque, even if we assume for argument’s sake that it is actually a hair of the Prophet (blessings and peace of Allah be upon him) and is proven by an unbroken, sound chain of narration.

Congratulating someone else on the occasion of his or her birthday is a kind of participating and cooperating in this innovation, and imitating the disbelievers.