(39) باب الاِسْتِثْنَاءِ .
It was narrated that Ibn 'Umar said:
"The Messenger of Allah said: 'Whoever swears an oath and says: If Allah wills, then he has made an exception.'"
Reference: Sunan an-Nasa'i 3829
In-book reference: Book 35, Hadith 69
English translation: Vol. 4, Book 35, Hadith 3860