باب ما جاء في شيب رسول الله صلى الله عليه وسلم
5  
Appearing Of The White Hair Of Rasoolullah
Ash-Shama'il Al-Muhammadiyah 39
Jabir ibn Samura was asked about the grayness of Allah’s Messenger (Allah bless him and give him peace), so he said:
"When he oiled his head, no grayness was visible, and when he did not apply oil, some was visible.”
حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، قَالَ‏:‏ أَخْبَرَنَا أَبُو دَاوُدَ، قَالَ‏:‏ حَدَّثَنَا شُعْبَةُ، عَنْ سِمَاكِ بْنِ حَرْبٍ، قَالَ‏:‏ سَمِعْتُ جَابِرَ بْنَ سَمُرَةَ، وَقَدْ سُئِلَ عَنْ شَيْبِ رَسُولِ اللهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّم، فَقَالَ‏:‏ كَانَ إِذَا دَهَنَ رَأْسَهُ لَمْ يُرَ مِنْهُ شَيْبٌ، وَإِذَا لَمْ يَدْهِنْ رُئِيَ مِنْهُ شَيْءٌ‏.‏
Grade: Sahih (Zubair Alizai)  صحيح   (Zubair Alizai) حكم   :
Reference : Ash-Shama'il Al-Muhammadiyah 39
In-book reference : Book 5, Hadith 3
Explanation
comments
Oil gives the hair a shine, therefore the white hair becomes indistinguishable from the other hair, or they become compact and mixed, therefore the few whit hairs cannot be easily seen. When there is no oil the hair becomes dry and loose, and is easily seen.
Hadith Text
Reference