Sa'id bin Jubayr heard Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) say: Whoever makes his wife forbidden (haram) for himself, that is an oath; he should give its expiation. "Indeed, in the Messenger of Allah (peace and blessings be upon him) you have an excellent example" [Surah al-Ahzab: 21].
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الخلع والطلاق / 15054