The Ruling on Returning the Salam to One Who Does Not Return It

Question:
What is your opinion of those who greet you but do not return the salam?

Answer:
Greeting with the salam is a recommended practice (sunnah). Returning the salam is obligatory (wajib). Therefore, whoever does not return the salam commits a sin, because he has abandoned an obligation, and thus he is sinful. It is not permissible for a Muslim to boycott his brother or not to return his salam, except if he did not hear it. If he knew that he was supposed to hear it, then he should listen for the salam. It is not permissible for a Muslim to listen and not return the salam, or to have something in his heart against the person, or for a person to be in a state that does not allow him to return the salam. For example, a person who is praying, or a person who is reciting the Qur'an; one does not greet him while he is reciting the Qur'an, because this would interrupt his recitation. Or if someone enters while people are listening to the Friday sermon, one does not greet him, and if he does greet, it is not returned, because the Prophet (peace and blessings be upon him) forbade speaking. There are situations in which it is not permissible to return the salam, or a person is attending to his needs, or one does not greet him while he is attending to his needs. There are situations in which a person is not allowed to return the salam.
Did you hear? This questioner encountered one of these situations in which it is not permissible to return the salam, and also his companion boycotted him or held a grudge against him. Yes?
Regarding returning the salam: if someone greets you, you return it to him, even if he is an innovator (mubtadi'). You do not initiate the salam to him, but if he greets you, you return it. Even if a disbeliever, a Christian, initiates the salam, or a Jew or Christian initiates the salam, we return it, saying what the Prophet (peace and blessings be upon him) commanded us to say: "And upon you."