Sayyiduna Ali (may Allah be pleased with him) states: The Messenger of Allah (peace and blessings be upon him) sent me to Yemen. I said: "O Messenger of Allah, I am a young man and I have no knowledge of judging?" He (peace and blessings be upon him) said: "Go, Allah will guide you and keep your tongue firm." After that, I never felt any doubt in judging between two men.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النذور / 20154