Question:
Asalamualaikum, hope you are well.
In Shaykh Abdulqadir Jaylani rahimahullah and Saeed ibn Musayyib rahimahullah‘s seerah it says both prayed Fajr with the wudu of Isha because of tahajjud. My question is when would they sleep and how many hours?
Answer:
Waalaikumussalam warahmatullah.
Tahajjud by definition involves rising from sleep. However wudu‘ is not lost from a light sleep while sitting. Many of the Salaf were observed practicing that even when travelling. Regardless it is not a question of hours or timing but of state and maqam.
Hajj Gibril Haddad