(7) باب نَهْيِ مَنْ دَخَلَ عَلَيْهِ عَشْرُ ذِي الْحِجَّةِ وَهُوَ مُرِيدُ التَّضْحِيَةِ أَنْ يَأْخُذَ مِنْ شَعْرِهِ أَوْ أَظْفَارِهِ شَيْئًا
Umm Salama reported Allah's Messenger (ﷺ) having said this:
When any one of you intending to sacrifice the animal enters in the month (of Dhu'l-Hijja) he should not get his hair or nails touched (cut). It was said to Sufyan that some of the (scholars) did not deem this hadith to be Maffu'. He said: But I deem it as Marfu' (i. e. chain of narration traceable right up to the Holy Prophet).
Reference: Sahih Muslim 1977 c
In-book reference: Book 35, Hadith 53
USC-MSA web (English) reference(deprecated numbering scheme): Book 22, Hadith 4869