The Messenger of Allah ﷺ most often swore by the words, "No, by the One who turns the hearts."
حدثنا أبو إسحق الشافعي إبراهيم بن محمد بن العباس حدثنا عبد الله بن رجاء المكي عن عباد بن إسحق عن ابن شهاب
كانت أكثر أيمان رسول الله ﷺ لا ومصرف القلوب
No references are available.
Its isnad is daif. Nasai narrated it in Al-Ayman wal-Nudhur, Al-Half bi-Musarrifil-Qulub, no. 3793, from the hadith of Abdullah bin Raja with this wording. It contains several flaws, among them the use of an ambiguous transmission form (an'ana) by Zuhri. Bukhari narrated, no. 6617, and others, from Abdullah bin Umar, who said, "The Prophet would often swear, 'No, by the One who turns the hearts.'" This is the correct version.