A speaker gave sermon before the prophet (May peace be upon him). He said : he who obeys Allah and his Prophet will follow the right course, and he who disobeys them. He (The prophet) said: get up; he said: go away, a bad speaker you are.  

أَنَّ خَطِيبًا خَطَبَ عِنْدَ النَّبِيِّ ﷺ فَقَالَ مَنْ يُطِعِ اللَّهَ وَرَسُولَهُ فَقَدْ رَشَدَ وَمَنْ يَعْصِهِمَا فَقَالَ قُمْ أَوْ قَالَ اذْهَبْ فَبِئْسَ الْخَطِيبُ أَنْتَ  

I was riding on a mount behind the prophet (May peace be upon him). It stumbled. Thereupon I said: May the devil perish! He said: do not say; may the devil perish! For you say that, he will swell so much so that he will be like a house, and say: by my power. But say: in the name of Allah; for when you say that, he will diminish so much so that he will be like a fly.  

كُنْتُ رَدِيفَ النَّبِيِّ ﷺ فَعَثَرَتْ دَابَّتُهُ فَقُلْتُ تَعِسَ الشَّيْطَانُ فَقَالَ لاَ تَقُلْ تَعِسَ الشَّيْطَانُ فَإِنَّكَ إِذَا قُلْتَ ذَلِكَ تَعَاظَمَ حَتَّى يَكُونَ مِثْلَ الْبَيْتِ وَيَقُولَ بِقُوَّتِي وَلَكِنْ قُلْ بِسْمِ اللَّهِ فَإِنَّكَ إِذَا قُلْتَ ذَلِكَ تَصَاغَرَ حَتَّى يَكُونَ مِثْلَ الذُّبَابِ  

The Prophet ﷺ said: When you hear....(Musa's version has): When a man says people have perished, he is the one who has suffered that fate most. Abu Dawud said: Malik said: If he says that out of sadness for the decadence of religion which he sees among the people, I do not think there is any harm in that. If he says that out of self-conceit and servility of the people, it is an abominable act which has been prohibited.  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ إِذَا سَمِعْتَ وَقَالَ مُوسَى إِذَا قَالَ الرَّجُلُ هَلَكَ النَّاسُ فَهُوَ أَهْلَكُهُمْ