Sahih Al Bukhari Hadith Number 814

Narrated Sahl bin Sa`d: The people used to pray with the Prophet (peace be upon him) tying their Izars around their necks because of their small sizes and the women were directed that they should not raise their heads from the prostrations till the men had sat straight.

10  Call to Prayers (Adhaan)
Hadith number 814
Volume no 1
Chapter: 136 (To tie the clothes and wrap them properly [in Salat (prayer)]; and whoever gathered his clothes for fear that his private parts may become exposed.)