May one greet a person who is performing ablution?
Giving salam is one of the most important symbols of our religion. Prophet Muhammad informed us that exchanging salams will spread love among Muslims. (Abu Dawud, Adab, 143). However, it is not permissible to give salam to the people who are not in a suitable position to respond salam. For example, it is makruh to give salam to people who are reciting adhan and Holy Qur’an, delivering or listening to the sermon. It is more appropriate not to give salam to the people who are performing ablution for it is considered as preparation to worship and as a worship in a way.
Source: Presidency Of Religious Affairs The Turkey, High Board of Religious Affairs FATWAS