The Prophet ﷺ told us that Shaytan would whisper questions such as "Who created your Lord?", and taught that the believer should seek refuge in Allah (SWT) and stop dwelling on them (Sahih al-Bukhari 3276). Whispers that trouble you are not a sign of lost faith; turning to Allah (SWT) is the answer.
Amantu billahi wa rusulih
“I believe in Allah and His messengers.”
The Prophet ﷺ taught this for the one troubled by whispers about faith.
Huwa-l-Awwalu wa-l-Akhiru wa-dh-Dhahiru wa-l-Batin, wa huwa bi-kulli shay'in 'Alim
“He is the First and the Last, the Most High and the Most Near, and He has full knowledge of all things.”
Ibn 'Abbas advised reciting this verse when a doubt finds its way into the heart.