What was the official language of the Umayyad Caliphate?

What was the official language of the Umayyad Caliphate?

اموی خلافت کی سرکاری زبان کیا تھی؟
Explanation

The Umayyad Caliphate  was the second of the four major caliphates established after the death of Muhammad.

The caliphate was ruled by the Umayyad dynasty  "Sons of Umayyah".

The third caliph of the Rashidun Caliphate, Uthman ibn Affan was also a member of the Umayyad clan.