Imam al-Shafi'i (may Allah have mercy on him) said: It has reached me that Sayyiduna Umar (may Allah be pleased with him) swore an oath on the minbar in a dispute that was between him and a man, and that the oath was turned back onto Sayyiduna Uthman (may Allah be pleased with him) at the minbar, but he avoided it and paid a ransom to be free of it, saying: I fear that it may coincide with a decreed affliction, and it will be said: (This is) because of his oath.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20698