Sunan Ibn Majah 2105
سنن ابن ماجه#2105SahihIt 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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Fouad Abd al-BaqiSahih
Shuaib Al ArnautSahih
Zubair Ali ZaiIsnaad Sahih
In-book reference: 11:16