"Some Bedouins asked: 'O Messenger of Allah (s.a.w) shall we treat (our ill)?' He said: 'Yes, O worshipers of Allah! Use remedies. For indeed Allah did not make a disease but He made a cure for it' - or - 'a remedy. Except for one disease.' They said: 'O Messenger of Allah (s.a.w)! What is it?' He said: 'Old age.'"
Jami` at-Tirmidhi Book 28, Hadith 3