When he oiled his head nothing was seen (as a mark of old age) and when he did not apply oil something (of the old age) became visible. (Using translation from Muslim 2344a)
عَنْ شَيْبِ النَّبِيِّ ﷺ قَالَ «كَانَ إِذَا دَهَنَ رَأْسَهُ لَمْ يُرَ مِنْهُ وَإِذَا لَمْ يَدَّهِنْ رُئِيَ مِنْهُ»
When he oiled his head nothing was seen (as a mark of old age) and when he did not apply oil something (of the old age) became visible.
عَنْ شَيْبِ النَّبِيِّ ﷺ فَقَالَ كَانَ إِذَا دَهَنَ رَأْسَهُ لَمْ يُرَ مِنْهُ شَىْءٌ وَإِذَا لَمْ يَدْهُنْ رُئِيَ مِنْهُ
"I heard Jabir bin Samurah being asked about the gray hairs of the Prophet [SAW]. He said: 'If he put oil on his head they could not be seen, but if he did not put oil on his head, they could be seen.'"
عَنْ شَيْبِ رَسُولِ اللَّهِ ﷺ قَالَ كَانَ إِذَا ادُّهِنَ رَأْسُهُ لَمْ يُرَ مِنْهُ وَإِذَا لَمْ يُدَّهَنْ رُئِيَ مِنْهُ