Sahih Bukhari Volume 9, Book 92, Hadith Number 377.

Narrated By Abdullah bin Dinar : ‘Abdullah Bin ‘Umar wrote to ‘Abdul Malik bin Marwan, swearing allegiance to him: ‘I swear allegiance to you in that I will listen and obey what is in accordance with the Laws of Allah and the Tradition of His Apostle as much as I can.’