I have repented. But in my possession are some forbidden things such as musical instruments, cassettes, films, etc. Is it permissible for me to sell them, particularly since they are worth a large amount?
Sale of such banned articles is not permissible in Islam. The Prophet (peace and blessings of Allah be upon him) said: “When Allah forbids a thing, then He forbids its price (as well).” (i.e., its sale/purchase/trading.) [Abu Dawood, and it is authentic] Also, you know well that whomever you sell it to will use it in a forbidden act; thus, it is not permissible for you to sell it to him as Allah has prohibited this in commanding us (in meaning): ‘do not assist one another in sins and enmity’.
And no matter how much you lose in worldly wealth, have faith that what is in store with Allah is worthier and longer lasting. He will compensate you with His grace, and His favor and His generosity.
And Allah knows best.