Sahih Bukhari Volume 8, Book 73, Hadith Number 88.

Narated By Salim: That his father said; “When Allah’s Apostle mentioned what he mentioned about (the hanging of) the Izar (waist sheet), Abu Bakr said, “O Allah’s Apostle! My Izar slackens on one side (without my intention).” The Prophet said, “You are not among those (who, out of pride) drag their Izars behind them.”