Sahih Al Bukhari Hadith Number 816

Narrated Ibn `Abbas: The Prophet (peace be upon him) said, “I have been ordered to prostrate on seven (bones) and not to tuck up the hair or garment.”

10  Call to Prayers (Adhaan)
Hadith number 816
Volume no 1
Chapter: 138 (One should not tuck up his garment in As-Salat (the prayer)