مختصر صحيح بخاري
Mukhtasar Sahih Bukhari
Book of Wudu (Ablution)
Considering ablution obligatory only after discharge from front or back
Narrated Abu Huraira (may Allah be pleased with him): The Messenger of Allah (peace and blessings of Allah be upon him) said: "A servant remains in the state of prayer as long as he is waiting for the prayer in the mosque, unless he loses his ablution."