Sahih Muslim
The Book Pertaining to the Excellent Qualities of the Holy Prophet (may Peace be upon them) and His Companions (Kitab Al-Fadail)
Book Number: 030 / Hadith Number: 5788
Jabir b. Samura was asked about the old age of Allah's Apostle (may peace be upon him). He said: 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.