Al-Zuhri (may Allah have mercy on him) said that Abu Bakr al-Siddiq (may Allah be pleased with him) said: "If I found a man committing one of the hadd offences of Allah, I would neither apply the hadd to him myself nor summon anyone against him until someone else was with me."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20505