Urwah bin al-Zubayr (may Allah have mercy on him) said that a man took khul' from his wife during the caliphate of Uthman (may Allah be pleased with him) without going before a ruler, and Uthman (may Allah be pleased with him) declared it valid.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الخلع والطلاق / 14859