Tafsir of Al-Ikhlas 112:1

The reason for the revelation of this Surah has already been mentioned. Ikrimah said, "When - the Jews said, `We worship Uzayr, the son of Allah,' and - the Christians said, `We worship the Messiah (Isa), the son of Allah,' and - the Zoroastrians said, `We worship the sun and the moon,' and - the idolators said, `We worship idols,' Allah revealed to His Messenger,

قل هو الله أحد

Say: "He is Allah, One.'' meaning, - He is the One, the Singular, - Who has no peer, - no assistant, no rival, - no equal and none comparable to Him. This word (Al-Ahad) cannot be used for anyone in affirmation except Allah the Mighty and Majestic, because He is perfect in all of His attributes and actions. Concerning His saying,

الله الصمد