The Messenger of Allah (may Allah's peace and blessings be upon him) recited: {Say, “O disbelievers”} and {Say: “He is Allah, the One”} in the two Rak‘ahs of Fajr

Explanation

The Prophet (may Allah's peace and blessings be upon him) used to prefer reciting {Say, “O disbelievers} [Surat al-Kāfirūn] in the first Rak‘ah of the Fajr confirmed voluntary prayer, after reciting Surat al-Fātihah, and {Say: “He is Allah, the One} [Surat al-Ikhlās] in the second Rak‘ah.

Benefits

• It is recommended to recite these two Surahs after Surat al-Fātihah in the Sunnah of Fajr.
• Each of these two Surahs is called "Surat al-Ikhlās" (sincerity), given that Surat al-Kāfirūn includes a declaration of disassociation from everything the polytheists worship apart from Allah, besides the indication that they are not also slaves of Allah because their Shirk (polytheism) renders their deeds worthless, and the fact that Allah Almighty is the only One worthy of worship. Moreover, Surat al-Ikhlās declares the oneness of Allah, emphasizes sincerity to Him, and clarifies His attributes.