Sahih al-Bukhari 3546
Sahih al-Bukhari · Book 61: Virtues and Merits of the Prophet (pbuh) and his Companions · The description of the Prophet (saws)
Narrated Hariz bin `Uthman:
حَدَّثَنَا عِصَامُ بْنُ خَالِدٍ ، حَدَّثَنَا حَرِيزُ بْنُ عُثْمَانَ ، أَنَّهُ سَأَلَ عَبْدَ اللَّهِ بْنَ بُسْرٍ صَاحِبَ النَّبِيِّ صلى الله عليه وسلم قَالَ أَرَأَيْتَ النَّبِيَّ صلى الله عليه وسلم كَانَ شَيْخًا قَالَ كَانَ فِي عَنْفَقَتِهِ شَعَرَاتٌ بِيضٌ.
That he asked `Abdullah bin Busr (i.e. the companion of the Prophet), "Did you see the Prophet (ﷺ) when he was old?" He said, "He had a few white hairs between the lower lip and the chin."