Sahih al-bukhari:5252 Chapter: “O Prophet! When you divorce women, divorce them at their ‘Idda and count their ‘Idda.” Book 68, Hadith 2

Narrated Anas bin Seereen: Ibn `Umar said: “I divorced my wife while she was menstruating. `Umar mentioned that to the
Prophet . The Prophet (ﷺ) said, (to my father), “Let your son take her back.” I asked (Ibn `Umar), “Is such
a divorce counted (i.e. as one legal divorce)?” Ibn `Umar said, “Of course.” Narrated Yunus bin
Jubair: Ibn `Umar said, “The Prophet (ﷺ) said to `Umar, ‘Order him (Ibn `Umar) to take her back.’ ” I
asked, “Is such a divorce counted (as one legal divorce)?” Ibn `Umar said, “What do you think if
someone becomes helpless and foolish?”