Abu Dawud Book 36, Hadith Number 5115.

Narated By al-Ala’ ibn al-Hadrami : Some of the children of al-Ala’ ibn al-Hadrami said: Al-Ala’ ibn al-Hadrami was the governor of the Prophet (PBUH) at al-Bahrayn, and when he wrote to him he began with his won name.