Hadithcore
Mishkat al-Masabih, 3422

Abu Sa'id al-Khudri told that when God’s Messenger swore strongly he said, “No, by Him in whose hand is the soul of Abu Qasim.” Abu Dawud transmitted it.

وَعَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ قَالَ: كَانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِذَا اجْتَهَدَ فِي الْيَمِينِ قَالَ: «لَا وَالَّذِي نفس أَبُو الْقَاسِم بِيَدِهِ» . رَوَاهُ أَبُو دَاوُد

References1 variant
In-Book Reference
Book 15, Hadith 17