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  • Part_one_Explanation_of_Koran_and_Al_Fatihah, page : 23

Therefore, whoever of you witnesses the month, let him fast.

But he who is ill, or on a journey shall (fast) a similar number (of days) later on.
Allah wants ease for you and does not want hardship for you.

And that you fulfill the number of days and exalt Allah who has guided you
in order that you be thankful." 2:185

"Then, let the pilgrims accomplish their acts of cleansing,

and let them fulfill their vows, and circumambulate the Ancient House." 22:29

"Believers, fear Allah.

Let every soul look to what it has forwarded for the future,
and fear Allah, for Allah is Aware of the things you do." 59:18

It is very clear that the word "do" which appears in the preceding verses means there is
an obligation to do something.