From Sahih Muslim (Hadith 5119):
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: Muslim 5119