It was narrated from Abu Hurairah that the Messenger of Allah (ﷺ) said:
'Whoever swears an oath and says In sha' Allah, he will have made an exception."(2) (RU)
English reference (RU): Vol. 3, Book 11, Hadith 2104 (RU)
Arabic reference (RU): Book 11, Hadith 2182 (RU)