Sayyiduna Qurrah bin Iyas (may Allah be pleased with him) said: Sayyiduna Ibn Mas'ud (may Allah be pleased with him) had climbed a tree and was picking fruit from it for them. The wind blew and uncovered both his shins, and the people began to laugh at the thinness of his shins. The Messenger of Allah (peace and blessings be upon him) said: "By the One in whose hand is my soul! These two shins will be heavier in the Balance on the Day of Resurrection than the mountain of Uhud."
Hadith Referenceالمعجم الكبير للطبراني / باب القاف / 16109