Hadithcore
Sahih al-Bukhari, 6719
sahih

Narrated Hammad:

the same narration above (i.e. 709), "I make expiation for my dissolved oath, and I do what is better, or do what is better and make expiation."

حَدَّثَنَا أَبُو النُّعْمَانِ، حَدَّثَنَا حَمَّادٌ، وَقَالَ، ‏"‏ إِلاَّ كَفَّرْتُ يَمِينِي، وَأَتَيْتُ الَّذِي هُوَ خَيْرٌ ‏"‏‏.‏ أَوْ ‏"‏ أَتَيْتُ الَّذِي هُوَ خَيْرٌ، وَكَفَّرْتُ ‏"‏‏.‏

References2 variants
In-Book Reference
Book 84, Hadith 12
USC-MSA web (English) reference
Vol. 8, Book 79, Hadith 710 (deprecated numbering scheme)