The Book of Oaths and Vows
35/30. Chapter:
Vows Which Are Not Meant For The Face Of Allah
Sunan an-Nasai
أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ الأَعْلَى، قَالَ حَدَّثَنَا خَالِدٌ، عَنِ ابْنِ جُرَيْجٍ، قَالَ حَدَّثَنِي سُلَيْمَانُ الأَحْوَلُ، عَنْ طَاوُسٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ مَرَّ رَسُولُ اللَّهِ صلى الله عليه وسلم بِرَجُلٍ يَقُودُ رَجُلاً فِي قَرَنٍ فَتَنَاوَلَهُ النَّبِيُّ صلى الله عليه وسلم فَقَطَعَهُ قَالَ إِنَّهُ نَذْرٌ .
It was narrated that Ibn 'Abbas said: "The Messenger of Allah passed by a man who was leading another man by a rope. The Prophet took it, and cut it, and he said: 'It is a vow.'"
Reference : Sunan an-Nasa'i 3810In-book reference : Book 35, Hadith 50English translation : Vol. 4, Book 35, Hadith 3841