(1) باب وَقْتِ الطَّلاَقِ لِلْعِدَّةِ الَّتِي أَمَرَ اللَّهُ عَزَّ وَجَلَّ أَنْ تُطَلَّقَ لَهَا النِّسَاءُ
It was narrated from Ibn 'Abbas, concerning the saying of Allah, the Mighty and Sublime:
"O Prophet! When you divorce women, divorce them at their 'Iddah (prescribed periods)." Ibn 'Abbas, may Allah be pleased with him, said: "Before their 'Iddah elapses."
Reference: Sunan an-Nasa'i 3393
In-book reference: Book 27, Hadith 5
English translation: Vol. 4, Book 27, Hadith 3422