Ishaq bin Ibrahim (Ibn Rahwayh) says: The narration that the Prophet (peace be upon him) used to pray thirteen rak‘ahs of witr means that he used to pray thirteen rak‘ahs of tahajjud (qiyam al-layl) including witr, so in this, qiyam al-layl (tahajjud) has also been called witr. He has narrated a hadith from Aisha (may Allah be pleased with her) in this regard, and has also taken evidence from the saying of the Prophet (peace be upon him): "O people of the Qur’an! Pray witr." Ibn Rahwayh says that by this, the Prophet (peace be upon him) meant qiyam al-layl, and qiyam al-layl is only obligatory upon those who believe in the Qur’an (not upon followers of other religions).