Sahih Muslim 2361
The Book of Virtues
The Obligation To Obey What He Says With Regard To Matters Of Religion, But Not What He Says With Regard To Worldly Matters
Musa b. Talha reported: I and Allah's Messenger (ﷺ) happened to pass by people near the date-palm trees. He (the Prophet) said: What are these people doing? They said: They are grafting, i. e. they combine the male with the female (tree) and thus they yield more fruit. Thereupon Allah's Messenger (ﷺ) said: I do not find it to be of any use. The people were informed about it and they abandoned this practice. Allah's Messenger (ﷺ) (was later) on informed (that the yield had dwindled), whereupon he said: If there is any use of it, then they should do it, for it was just a personal opinion of mine, and do not go after my personal opinion; but when I say to you anything on behalf of Allah, then do accept it, for I do not attribute lie to Allah, the Exalted and Glorious.