Sahih Muslim
The Book Concerning the Use of Correct Words (Kitab Al-Alfaz min Al-Adab wa Ghairiha)
Book Number: 027 / Hadith Number: 5593
This hadith has been reported on the authority of al-A'mash with the same chain of transmitters, and the words are that the servant should not say to his chief: My Lord, and Abu Mu'awiya made an addition:" For it is Allah, the Exalted and Glorious, Who is your Lord."