Sunan Ibn Majah, Volume 4, Book 32, Hadith 3628 (DarusSalam) ⓘ
It was narrated that Abu Juhaifah said: “I saw the Messenger of Allah, and this part of his hair was white” – meaning the tuft of hair between the lower lip and the chin.
حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا أَبُو دَاوُدَ، حَدَّثَنَا زُهَيْرٌ، عَنْ أَبِي إِسْحَاقَ، عَنْ أَبِي جُحَيْفَةَ، قَالَ رَأَيْتُ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ هَذِهِ مِنْهُ بَيْضَاءُ . يَعْنِي عَنْفَقَتَهُ .
also referenced under: Hadith 3628 (Reference) & Book 32, Hadith 3759 (In-Book)