Musnad Ahmad 25:1016

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from Ibn Tawus, from his father, from Ibn 'Abbas, who said: "Divorce during the time of the Messenger of Allah (peace be upon him), Abu Bakr, and two years of the caliphate of 'Umar ibn al-Khattab, the three divorces were [counted as] one." Then 'Umar said: "Indeed, the people have made haste in a matter in which they had leeway, so if we were to enforce it upon them." So he enforced it upon them.