The Messenger of Allah ﷺ said, "When one of you takes an oath, he should not say, 'Whatever Allah wills and you will,' but rather he should say, 'Whatever Allah wills, then what you will.'"
قال رسول الله ﷺ: إذا حلف أحدكم فلا يقل: ما شاء الله وشئت، ولكن ليقل: ما شاء الله ثم شئت.
Ibn Majah (2117), Nasai in Amal al-Yawm wal-Layla (988), Ahmad (1839), and Bayhaqi (3/217) all narrated it through the route of Ajlah Kindi, from Yazid bin Asam, from Ibn Abbas, who related it, and the wording given is that of Ibn Majah. Its chain is hasan because of Ajlah Kindi, who is Yahya bin Abdullah, concerning whom there is disagreement, but his hadith is hasan. There are other hadiths on this subject which I have discussed in the book on faith.