Sahih Al Bukhari Hadith Number 727

Narrated Anas bin Malik: One night an orphan and I offered the prayers behind the Prophet (peace be upon him) in my house and my mother (Um Sulaim) was standing behind us (by herself forming a row).

10  Call to Prayers (Adhaan)
Hadith number 727
Volume no 1
Chapter: 78 (One woman can form a row)