Tafsir of Ghafir 40:65

He is the Ever-Living (the One unique in true, self-subsisting life), there is no god but Him (as there is no existing being that approaches Him in His essence, His attributes, and His actions, Mighty and Majestic is He). So call upon Him (so worship Him exclusively, for no one else possesses the attributes that necessitate such worship). The interpretation of "calling upon" as "worship" is what is required by His saying: "making the religion sincere for Him"—that is, obedience, free from both hidden and manifest polytheism. This is the most appropriate interpretation to follow the aforementioned descriptions of Lordship and Divinity. It was mentioned under the title of "calling upon" because the most befitting manner of worship is that which is done with supplication, brokenness, and humility. Praise be to Allah, Lord of the worlds.

(That is, saying that). Ibn Jarir, Ibn al-Mundhir, al-Hakim (who authenticated it), and al-Bayhaqi in al-Asma’ wa al-Sifat narrated from Ibn Abbas that he said: "Whoever says 'There is no god but Allah,' let him follow it immediately with 'Praise be to Allah, Lord of the worlds,' and that is His saying: 'So call upon Him, making the religion sincere for Him,' etc." Abd ibn Humayd narrated something similar from Sa’id ibn Jubayr. According to this, "Praise be to Allah, Lord of the worlds" is part of the speech of those who were commanded to worship prior to it. It is also permitted that it be from the speech of Allah Almighty, as an initiation of praise of His own Essence by His own Essence, Mighty and Majestic is He.