Sahih Bukhari Volume 9, Book 89, Hadith Number 310.

Narrated By ‘Abdullah bin Dinar : I witnessed Ibn ‘Umar when the people gathered around ‘Abdul Malik. Ibn ‘Umar wrote: I gave the Pledge of allegiance that I will listen to and obey Allah’s Slave, ‘Abdul Malik, Chief of the believers according to Allah’s Laws and the Traditions of His Apostle as much as I can; and my sons too, give the same pledge.’