Sunan Ibn Majah, Volume 4, Book 32, Hadith 3629 (DarusSalam) ⓘ

It was narrated that Humaid said: “Anas bin Malik was asked: ‘Did the Messenger of Allah dye his hair?’ He said: ‘He did not have any white hair apart from approximately seventeen or twenty hairs at the front of his beard.’”

حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا خَالِدُ بْنُ الْحَارِثِ، وَابْنُ أَبِي عَدِيٍّ، عَنْ حُمَيْدٍ، قَالَ سُئِلَ أَنَسُ بْنُ مَالِكٍ أَخَضَبَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ قَالَ إِنَّهُ لَمْ يَرَ مِنَ الشَّيْبِ إِلاَّ نَحْوَ سَبْعَةَ عَشَرَ أَوْ عِشْرِينَ شَعَرَةً فِي مُقَدَّمِ لِحْيَتِهِ ‏.‏