It was narrated from Ibn 'Umar that the Messenger of Allah (ﷺ) said:
"Whoever swears an oath and says In sha' Allah, if he wishes he may go ahead and if he wishes he may not, without having broken his oath." (IT)
English reference (IT): Vol. 3, Book 11, Hadith 2105 (IT)
Arabic reference (IT): Book 11, Hadith 2183 (IT)