Umar (ra) is reported to have stood on the minbar and demanded that the mahr be lowered, a woman stood up and refuted him with the book of Allah, he humbly said a woman is right and umar is wrong.
Umar is reported to have stood for khutbah and repeated the words of the messenger of Allah "whomsoever Allah guides, there is none to misguide, and whomsoever Allah causes to go astray- there is none to guide",
A man stood up and retorted (from his whim): Allah does not misguide anyone!
Umar said: If you say that again, I will kill you. (full stop with emphasis).
A man at one of the Muslim battle fronts was going around and asking useless and non-beneficial questions like what does azzaariyaati Zar'a mean, what does annaashitaati nashtaa mean, to the extent that the generals and commanders became worried about fitnah among the new Muslims to the extent that they sent a request to ameerul my-mineen umar, he asked that the man be sent to medina.
When the man arrives in the mosque umar (ra) asks: I hear you have some questions, the man begins repeating his silly year ions and umar says yes go on, go on until he finishes,
Umar then orders a carpet to be brought and rolls the man in the carpet and starts beating it with his famous stick, do you know the answer to your questions?
Yes yes ameerul mu-mineen, I know the answer.

The man never asked those questions until umar died, and then apparently started asking again.
I'll post sources when I'm on a pc inshaAllah-unless someone manages first.
هُوَ الَّذى أَنزَلَ عَلَيكَ الكِتٰبَ مِنهُ ءايٰتٌ مُحكَمٰتٌ هُنَّ أُمُّ الكِتٰبِ وَأُخَرُ مُتَشٰبِهٰتٌ ۖ فَأَمَّا الَّذينَ فى قُلوبِهِم زَيغٌ فَيَتَّبِعونَ ما تَشٰبَهَ مِنهُ ابتِغاءَ الفِتنَةِ وَابتِغاءَ تَأويلِهِ ۗ وَما يَعلَمُ تَأويلَهُ إِلَّا اللَّهُ ۗ وَالرّٰسِخونَ فِى العِلمِ يَقولونَ ءامَنّا بِهِ كُلٌّ مِن عِندِ رَبِّنا ۗ وَما يَذَّكَّرُ إِلّا أُولُوا الأَلبٰبِ
He it is Who has sent down to thee the Book: In it are verses basic or fundamental (of established meaning); they are the foundation of the Book: others are allegorical.
But those in whose hearts is perversity follow the part thereof that is allegorical, seeking discord, and searching for its hidden meanings, but no one knows its hidden meanings except Allah. And those who are firmly grounded in knowledge say: \"We believe in the Book; the whole of it is from our Lord:\" and none will grasp the Message except men of understanding.
Quran 3:7
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