It was narrated that Rifa'ah Al - Juhani said:
"When the Prophet (ﷺ) took an oath he would say: 'By the One in Whose Hand is the soul of Muhammad."' (TR)
English reference (TR): Vol. 3, Book 11, Hadith 2090 (TR)
Arabic reference (TR): Book 11, Hadith 2168 (TR)