The Noble Shaykh Dr. Ahmad Bāzmūl حفظه الله stated:
The Scholars of Tafsīr have agreed that the statement of Allāh:
وَاعْبُدْ رَبَّكَ حَتَّىٰ يَأْتِيَكَ الْيَقِينُ[Hijr 15:99]
Worship your Lord until the certainty
It means death. For that, the Sunnī defends the Sunnah until he dies. He refutes the false speech which opposes the Sunnah and Ijmā' (consensus) like the one who explained "certainty" (in the verse) to mean "faith". His statement is falsehood.