What does Islam say regarding selling poetry to music producers?

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, sallallaahu ʻalayhi wa sallam, is His slave and Messenger. 

This is impermissible because it constitutes cooperation in sin and transgression; Allaah, The Exalted, says (what means): {And cooperate in righteousness and piety, but do not cooperate in sin and aggression.} [Quran 5:2]

We have previously underlined the religious ruling on music in fatwa 81545; please refer to it.

Allaah knows best.