﴿ فَتَوَلَّىٰ عَنْهُمْ وَقَالَ يَٰقَوْمِ لَقَدْ أَبْلَغْتُكُمْ رِسَٰلَٰتِ رَبِّى وَنَصَحْتُ لَكُمْ ۖ فَكَيْفَ ءَاسَىٰ عَلَىٰ قَوْمٍۢ كَٰفِرِينَ ﴾

“And he turned away from them, and said: "O my people! Indeed, I delivered unto you my Sustainer's message and gave you good advice: how, then, could I mourn for people who have denied the truth?"”

So he turned back on them and said ‘O my people I have conveyed to you the Messages of my Lord and advised you sincerely but you believe not so why should I grieve for a disbelieving people?’ the interrogative is meant rhetorically as a negation.