Is the prayer of one who works in a shop that sells cassette tapes containing hymns and songs invalidated, and what is the ruling on one who has an atom's weight of faith and love for Allah, His Messenger, and the Companions entering Hellfire?

Selling and trading in forbidden songs is unlawful. A Muslim must seek what is lawful in their earnings. The prayer of a song seller is valid if it meets the conditions of validity, and its acceptance is with Allah. Disobedient Muslims will enter Hellfire according to the extent of their disobedience if they do not repent, but they will not abide therein eternally, for the Prophet, peace and blessings be upon him, said: "Get out of the Fire whoever has in his heart the weight of a mustard seed of faith."