Sayyiduna Abdullah (may Allah be pleased with him) said: "I used to gather a tooth-stick (siwak) from the arak tree for the Messenger of Allah (peace and blessings be upon him), and the wind would bend me over, for my shins were thin. The people laughed, whereupon the Prophet (peace and blessings be upon him) said: 'Why do you laugh at the thinness of his shins? By the One in whose hand my soul is, they (his shins) will be heavier in the Scale than Mount Uhud.'"
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8420