Consider these verses:

And if you are in doubt about what We have sent down upon Our Servant [Muhammad], then produce a surah the like thereof and call upon your witnesses other than Allah, if you should be truthful.

Surah al Baqarah, verse 23

Exalted is He who took His Servant by night from al-Masjid al-Haram to al-Masjid al- Aqsa, whose surroundings We have blessed, to show him of Our signs. Indeed, He is the Hearing, the Seeing.

Surah al-Isra verse, 1

Blessed is He who sent down the Criterion upon His Servant that he may be to the worlds a warner.

Surah Furqan-1

And that when the Servant of Allah stood up supplicating Him, they almost became about him a compacted mass."

Surah Jinn-19

In these verses, Allah has declared Prophet Mohammed ﷺ as his Abd. Abdullah is derived from the term ‘Abd’ which means a slave or one who serves and Abdullah means one who serves, worships and obeys Allah. ‘Abd’ refers to someone who has a soul and body.

Why did Allah title His Messenger as ‘Abd’?

The pagans of Makkah believed that angels were the daughters of Allah. The Jews believed Prophet Uzair ﷺ was the son of Allah while the Christians considered Jesus ﷺ as the son of Allah. (The Christians still believe in it). All these creations of Allah are not His offspring rather they all are the worshippers of Allah. Since the Prophet Mohammed ﷺ is also the Prophet for Jews and Christians as well as for all mankind, the term son of god or god incarnated had to be strongly rebutted. That is why the term ‘Abd’ is used in Quran to establish the true status of our Prophet ﷺ.