Sahih Muslim
The Book of Virtue, Good Manners and Joining of the Ties of Relationship (Kitab Al-Birr was-Salat-I-wal-Adab)
Book Number: 032 / Hadith Number: 6184
Abdullah b. 'Anir reported that a person came to Allah's Apostle (may peace be upon him) and sought permission (to participate) in Jihad, whereupon he (the Holy Prophet) said: Are your parents living? He said: Yes. Thereupon he (the Holy Prophet) said: You should put in your best efforts (in their) service.