Surah 2, Verse 235

There is no harm in proposing in secret to (any of) these women, or keeping the intention to yourself: God is aware that you will keep them in mind. Yet do not make a promise in secret, unless you speak in a manner that is proper; and do not resolve upon marriage till the fixed term of waiting is over. Remember that God knows what is in your hearts; so be fearful of Him, and remember that God is forgiving and forbearing.

— Quran 2:235

Quote from Quran 2:235