Assalamu Alaikum!
Someone gave me a t-shirt for my birthday and I accepted it. Is it allowed for me to wear it?
How about accepting gift given on the day of someone's birthday?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

First of all, you should know that it is not permissible for a Muslim to celebrate his birthday as there is no proof for it in the religion of Islam. We have already discussed this in Fatwa 81725, so please refer to it.

Therefore, you should repent from doing such a celebration and you should not do it in the future.

As regards the gift, in principle, it is Islamically required and recommended to accept gifts because this achieves some religious objectives. However, you should not accept it on such occasion as by doing so, you are encouraging people to do so and you are acknowledging it. But if refusing it leads to harm, like causing the donor to hate you and keep away from you, then it is permissible to accept it and benefit from it.

Allaah Knows best.