From Sahih Bukhari (Hadith 7272):
Narrated `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
Reference: Bukhari 7272