Are those praying sinful for not returning the greeting while they are in prayer, or is the one who extends the greeting sinful, knowing that they cannot respond?

It is disliked to greet those engaged in prayer and other acts of worship, as it may distract them. This is contrary to what is better (khilāf al-awlā) but not forbidden (muharram), and there is no sin upon the one who greets (al-musallim) nor upon the praying person (al-musallī) who does not return the greeting. It is recommended for the praying person to return the greeting by gesturing. Some Maliki scholars have enumerated twenty-five situations where returning the greeting is not obligatory, among them are the praying person, the eater, the reciter (of Qur'an), the one remembering God (dhākir), the one relieving himself, the child, and the intoxicated person.