When any ibaadah is executed with piety and internal purification, it is fulfilled in the proper manner and it is also accepted even if it may be very little. It is therefore necessary for a Muslim to reform both his external and internal self because this is the means to salvation and success. A Muslim should not consider mere outward acts of ibaadah to the exclusion of internal purification to be sufficient for his salvation. If a person offers salaat abundantly with the intention that people would consider him to be a pious person and begin praising him, will he save himself from punishment? When in fact, salaat is such a thing that if it is fulfilled in the proper manner and with sincerity, solely for the pleasure of Allah Ta’ala he will save himself from that punishment which is meted out for abandoning salaat and will also be rewarded. How sad that this person destroyed this salaat for the purpose of show and praise. It is therefore necessary for him to cure these internal sicknesses or else he will be utterly destroyed because it is obvious that once a sickness gets worse and it is not treated, the person will be destroyed.
(Source: Behishti Zewar)
Hazrat Moulana Ashraf Ali Thanwi رحمه الله