What is the ruling on giving a friend a music cassette?

Giving a friend a music cassette is considered aiding him in disobeying Allah, for singing is forbidden by the Qur'an, the Sunnah, and the consensus of the Ummah. A Muslim must help his brother in goodness, as Allah Almighty says: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." One should promote divine listening instead of satanic, to earn reward, not sin.