Language:
كتاب المناقب
61  
Virtues and Merits of the Prophet (pbuh) and his Companions
(23)
Chapter: The description of the Prophet (saws)
(23)
باب صِفَةِ النَّبِيِّ صلى الله عليه وسلم
Sahih al-Bukhari 3546

Narrated Hariz bin `Uthman:

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."

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.‏
Reference : Sahih al-Bukhari 3546
In-book reference : Book 61, Hadith 55
USC-MSA web (English) reference : Vol. 4, Book 56, Hadith 746
  (deprecated numbering scheme)