Abu Dawud
Prayer
Book Number: 002 / Hadith Number: 1224
Narated By 'Aisha, Ummul Mu'minin : Ata' ibn AbuRabah asked 'Aisha: Can women offer prayer on a riding beast? She replied: They were not permitted to do so in hardship or comfort. Muhammad ibn Shu'ayb said: This (prohibition) applies to the obligatory prayers.