Is the first wife's consent necessary for the validity of a man's second marriage? And did the Messenger of Allah, may Allah bless him and grant him peace, reject Ali ibn Abi Talib's, may Allah be pleased with him, second marriage due to the absence of a reason, and is it a condition to have reasons for a second marriage, and what are they?

The first wife's approval of a second marriage is not a condition for the validity of the marriage, and the second marriage is not considered void if the first wife does not approve.

The Prophet, peace be upon him, forbade Ali from marrying the daughter of Abu Jahl while being married to his daughter Fatimah for two reasons: fear of discord for Fatimah due to jealousy, and combining the daughter of the Messenger of Allah with the daughter of an enemy of Allah. The Prophet, peace be upon him, said: "Indeed, Fatimah is from me, and I fear that she may be tempted in her religion... And indeed, I do not forbid what is lawful nor permit what is unlawful, but by Allah, the daughter of the Messenger of Allah and the daughter of the enemy of Allah shall never be joined together."

Polygyny is permissible, but it is conditioned upon justice between wives regarding sustenance, housing, and lodging. Whoever cannot be just is not permitted to practice polygyny, as Allah Almighty says: {But if you fear that you will not be able to deal justly, then [marry only] one}. Justice in love is not a condition because it is not within one's capacity.