From Sahih Muslim (Hadith 6127):
Rafi' b. Khadij reported that Allah's Messenger (ﷺ) came to Medina and the people had been grafting the trees. He said:What are you doing? They said: We are grafting them, whereupon he said: It may perhaps be good for you if you do not do that, so they abandoned this practice (and the date-palms) began to yield less fruit. They made a mention of it (to the Holy Prophet), whereupon he said: I am a human being, so when I command you about a thing pertaining to religion, do accept it, and when I command you about a thing out of my personal opinion, keep it in mind that I am a human being. 'Ikrima reported that he said something like this
Reference: Muslim 6127