Musnad Ahmad 1099:9

'Abd al-Razzaq narrated to us, Ma'mar informed us, from Ibn Khuthaym, from Abu al-Tufayl, and he mentioned the building of the Ka'bah during the Pre-Islamic period (Jahiliyyah). He said: Quraysh demolished it and began building it with stones from the valley, which the people of Quraysh carried on their necks. They raised it twenty cubits into the sky. While the Prophet, peace and blessings of Allah be upon him, was carrying stones from Ajyad and wearing a *namirah* (a striped garment), the *namirah* became too tight for him. He went to place the *namirah* on his shoulder, and his private parts became visible due to the smallness of the *namirah*. He was called out: "O Muhammad, cover your private parts." He was never seen naked after that.