Narrated Abdullah ibn Abbas: 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 This was then repealed (by a Quranic verse). Divorce is only permissible twice.
Hadith Referenceسنن ابي داود / كتاب تفريع أبواب الطلاق / 2195
Hadith Gradingالألبانی:حسن صحيح | زبیر علی زئی:إسناده حسن, أخرجه النسائي (3584 وسنده حسن)
Benefits and Issues: Before the revelation of instructions regarding divorce, people would continue to give divorce and take their wives back, and there was no limit or specified number for divorces. The Noble Qur’an restricted them to only three: two are revocable, and after the third, taking her back is not permissible.
Source: Sunan Abu Dawood – Commentary by Shaykh Umar Farooq Saeedi, Page: 2195