بُلُوغُ الْمَرَامِ
Bulugh al-Maram 1068
Marriage
وَلِأَحْمَدَ : مِنْ حَدِيثِ سَهْلِ بْنِ أَبِي حَثْمَةَ : { وَكَانَ ذَلِكَ أَوَّلَ خُلْعٍ فِي اَلْإِسْلَامِ } [1] .
Ahmad reported from Sahl bin Abu Hathma's Hadith that it was the first ever husband and wife separation for compensation in Islam.
Sunnah.com reference: Book 8, Hadith 118