Musnad Abu Ya'la al-Mawsili 152:242

Abu Khaythama narrated to us, Rawh ibn ‘Ubadah narrated to us, Hammad ibn Salamah narrated to us, from ‘Asim ibn Bahdalah, from Zirr ibn Hubaysh, from Ibn Mas‘ud, who said: I was gathering a *siwak* (tooth-stick) from the *arak* tree for the Messenger of Allah (may Allah bless him and grant him peace), and the wind was blowing him over. There was something [thin] about my shins, so the people laughed. The Messenger of Allah (may Allah bless him and grant him peace) said: "What makes you laugh?" They said: "The thinness of his shins." He said: "By the One in Whose hand is my soul, they are heavier on the Scale than Uhud."