Musnad Ahmad 2855

It was narrated that Ibn ‘Abbas (رضي الله عنه) said: At the time of the Messenger of Allah (ﷺ) and Abu Bakr, and for two years of ‘Umar’s caliphate, the threefold talaq was counted as one. Then ‘Umar (رضي الله عنه) said: The people have begun to be hasty in a matter in which they should be careful and deliberate. Now we should take them at their word. And he did that [i.e., counted the threefold talaq as three].