17. Muhammad ibn Yahya has narrated from Muhammad ibn al-Husayn from Muhammad ibn Yahya ibn Habib who has said the following: “I once wrote to abu al-Hassan, al-Rida’ , asking, ‘There is optional Salah (prayer) on me, when should I perform Qada’ (compensatory prayer for) such missed Salah (prayer)?’ He (the Imam) wrote to me in answer, ‘You can perform them whenever you like, during the day or night.’”