“I once said to abu ‘Abd Allah (a.s.), that I fast these three days of the month but perhaps I travel or become ill, am I required to complete its Qada’ (compensatory fast)? He (the Imam) said, ‘Qada’ (compensatory fast) is obligatory for obligatory fast which is missed. In the case of optional fast it is up to you.’ I then asked, ‘Is it up to one’s choice even when on a journey and in illness?’ He (the Imam) said, ‘In the case of illness Allah, most Majestic, most Glorious, has exempted you, but in the case of journey you can complete its Qada’ (compensatory fast) and if you did not do so it is not harmful.’”