Arqam bin Shurahbil narrates: I scratched my body while I was in prayer and my hand reached my private part. I mentioned this to Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him), and he said, laughing: "(Then) cut it off! Where will you separate it from yourself? It is only a piece of your own body."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9182