Is it compulsory to recite certain invocations while performing ablution?
Some sources include separate invocations to be recited while washing each organ in ablution (Nawavi, al-Adhkar, pp. 32-35). However, according to authentic narratives, Prophet Muhammad (saw) did not make a special dua while performing ablution. Therefore, it is not compulsory to recite these duas although they have good meanings. However, it is permissible to recite them.
According to the authentic narratives, Prophet Muhammad (saw) gave glad tidings that eight doors of heaven will be open for those who recite the following dua at the end of ablution,
“I testify that none has the right to be worshiped but Allah, there are no partners for Him. And I testify that Muhammad is His servant and Messenger. O Allah! Make me among the repentant, and make me among those who purify themselves.” and then he will be allowed to enter in whichever door he wants (Tirmidhi, Taharah, 41).
Source: Presidency Of Religious Affairs The Turkey, High Board of Religious Affairs FATWAS
Would An Ablution Be Valid If Only Its Required Acts Are Performed?
