(Annajm) 53 : 55
فَبِأَيِّ آلَاءِ رَبِّكَ تَتَمَارَىٰ
Then in which of your Lord’s sign you are doubting?
The sign mentioned in the verse refers the ability of Allah, verses, miracles, blessings, etc. This question addresses not to the Messenger, but to other mankind. That means by utilising the Confirming Truth Adhikr, all doubts should be cleared and should confirm that I am one in thousand believer. See explanation 11: 17; 15: 99; and 45: 31-32.