Ibn ‘Abbās (may Allah be pleased with him) reported: The (pronouncement) of three divorces during the lifetime of the Messenger of Allah (may Allah's peace and blessings be upon him) and that of Abu Bakr and two years of the caliphate of ‘Umar (was treated) as one. Then ‘Umar ibn al-Khattāb said: "Indeed, people hasten to a matter in which they used to act with deliberation. So if we would count them as three divorces," and he did that.
This Hadīth shows that the triple divorce that used to occur during the time of the Prophet, may Allah's peace and blessings be upon him; the Caliphate of Abu Bakr; and the two years of the caliphate of ‘Umar (may Allah be pleased with him) was considered as one divorce. That is, the three successive pronouncements of divorce would count as one. For example, if a man says to his wife: "You are divorced" three times at once, this counts as one consequential divorce. However, if a man said "You are divorced thrice," gathering the three times of divorce in a single statement, this was meaningless and of no effect, thus, it would count as a single incident of divorce. When people started to act ruthlessly with regard to divorce and used it excessively and flippantly, ‘Umar (may Allah be pleased with him) wanted to stop people from rushing to a triple divorce. Therefore, he counted the triple divorce as three incidents rather than one. The scholars said that the pronouncement of divorce that counted as three incidents of divorce during ‘Umar's time only counted as one before his time. That is because people would not resort to the triple divorce and rarely used it. However, during ‘Umar's time, people used it frequently, so ‘Umar made it effective and counted it as three.