The Prophet's role as a warner (Nadhir)

عَلَىٰ قَلْبِكَ لِتَكُونَ مِنَ ٱلْمُنذِرِينَ

Upon your heart, [O Muḥammad] - that you may be of the warners -

۞ قُلْ إِنَّمَآ أَعِظُكُم بِوَٰحِدَةٍ ۖ أَن تَقُومُوا۟ لِلَّهِ مَثْنَىٰ وَفُرَٰدَىٰ ثُمَّ تَتَفَكَّرُوا۟ ۚ مَا بِصَاحِبِكُم مِّن جِنَّةٍ ۚ إِنْ هُوَ إِلَّا نَذِيرٌ لَّكُم بَيْنَ يَدَىْ عَذَابٍ شَدِيدٍ

Say, "I only advise you of one [thing] - that you stand for Allāh, [seeking truth] in pairs and individually, and then give thought." There is not in your companion any madness. He is only a warner to you before a severe punishment.