Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: "Sayyiduna Yusuf (peace be upon him) and his mother were given two thirds of beauty, that is, of people's beauty in the face, the fairness of complexion and other than that. When a woman came to him, he would cover his face, fearing that she would fall into temptation."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8525