The oath that the Messenger of Allah ﷺ used to swear by was, "No, by the One who turns the hearts."
أخبرني محمد بن يحيى بن عبد الله قال حدثنا محمد بن الصلت أبو يعلى قال حدثنا عبد الله بن رجاء عن عباد بن إسحق عن الزهري
كانت يمين رسول الله ﷺ التي يحلف بها لا ومصرف القلوب
No references are available.
Its chain is daif. It was narrated by Ibn Majah in the Book of Expiations, chapter on the Oath that the Messenger of Allah ﷺ used to swear by, hadith no. 2092, from the hadith of Abdullah bin Raja Al-Makki, with this wording. It is also found in Al-Kubra, hadith no. 4704. The preceding hadith makes it unnecessary.