Ubaidullah bin 'Umar bin Hafs عبيد الله بن عمر بن حفص بن عاصم · The Chapters on Divorce

the Messenger of Allah divorced Hafsah then took her back.

the Messenger of Allah said: What is wrong with people who play with the limits imposed by Allah, and one of them says: "I divorce you, I take you back, I divorce you?"

"Divorce according to the Sunnah means divorcing her when she is pure, ( i.e., not menstruating) and without having had intercourse with her (during that cycle)."

the Messenger of Allah (ﷺ) said: "Allah has forgiven my nation for what they think of to themselves, so long as they do not act upon it or speak of it."