The Prophet (ﷺ) said: There are three things which, whether undertaken seriously or in jest, are treated as serious: Marriage, divorce and taking back a wife (after a divorce which is not final)
Sunan Abi Dawud Book 13, Hadith 20
← Previous Hadith I went out with Adi ibn Adi al-Kindi till we came to Mecca. He sent me to Safiyyah daughter of Shaybah who remembered a tradition (that she had heard) from Aisha. She said: I heard Aisha say: I heard the Messenger of Allah (ﷺ) say: There is no divorce or emancipation in case of constraint or duress (ghalaq).

Abu Dawud said: I think ghalaq means anger.

Sunan Abi Dawud Book 13, Hadith 19 Next Hadith → Divorced women shall wait concerning themselves for three monthly periods. Nor is it lawful for them to hide what Allah hath created in their wombs. This means that if a man divorced his wife he had the right to take her back in marriage though he had divorced her by three pronouncements. This was then repealed (by a Qur'anic verse). Divorce is only permissible twice.

Sunan Abi Dawud Book 13, Hadith 21