Ibn Tawus (may Allah have mercy on him) narrates from his father (may Allah have mercy on him) that he said: Whatever is intended as divorce is a divorce. The same has been narrated from Masruq (may Allah have mercy on him), Ibrahim (may Allah have mercy on him) and others, and what they meant by this is when he utters words resembling divorce.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الخلع والطلاق / 15015