O my dear son! I have fastened the load of pain and have warded off rebellion from you, and have straightened up matters. I have tamed the enemies, have brought the reins of the Arabs in your hands, and have accumulated that for you which no one has ever done. Thus consider the people of Hijaz, who are your foundation and your roots. Give respect to those among the people of Hijaz who come to you, and keep inquiring about those who are not present among them. Besides, consider the people of Iraq, and if they desire that you depose a Governor every day, do not refuse, for it is easy to change a Governor than to face ten thousand swords drawn forth facing you. Favor the people of Syria for they are your near-ones and your reservoirs, and if you fear an enemy, ask for their help. And when you have accomplished your goal (of defeating the enemy) return them back to the cities (of Syria), for if they remain elsewhere their manners will change. I do not fear anyone opposing or fighting with you on the question of Caliphate except four persons. Those being Husain bin Ali, Abdullah bin Umar, Abdullah bin Zubayr and son of Abu Bakr. As regards Abdullah bin Umar, (excessive) worship has broken him, if no one remains to assist him, he shall succumb to you. As regards Husain bin Ali, he is light-minded person, and the people of Iraq will betray him until they force him to rebel. If he revolts and you gain victory over him, excuse him, for he is linked to us through relation and he keeps greater right while having relation and nearness of the Holy Prophet. As regards the son of Abu Bakr, he follows that what his companions like and his aspiration are only women and play. While the one who like a Lion lies in ambush, and the Fox who is playing a game with you and is in track of an opportunity to pounce upon you is the son of Zubayr. And if he revolts and you gain victory over him, separate every joint of his. Try and keep safe the blood of our own people."
It is said that during the days of the illness and death of his father Mu’awiyah, Yazeed was not present in Syria. Hence Mu’awiyah called for Zahhak bin Qays and Muslim bin Uqba Murri and instructed them to hand over his will to Yazeed, while this seems quite acceptable.
source : tebyan