Does one commit a sin if he visits the grave of the Messenger (peace and blessings be upon him) and then does not greet the two Shaykhs, Abu Bakr and 'Umar?

Question:
May Allah reward you, Honorable Shaykh. This questioner says: In the statement of the author (may Allah have mercy on him), "greeting them is obligatory," meaning Abu Bakr and 'Umar, does the one who visits the grave of the Messenger (peace and blessings be upon him) and then does not greet the two Shaykhs, Abu Bakr and 'Umar, commit a sin?

Answer:
If he leaves that off out of dislike for them, then he commits a sin. If he leaves that off out of dislike for Abu Bakr and 'Umar, because some sects dislike Abu Bakr and 'Umar, and indeed it is mentioned that they spit on the grave of Abu Bakr and 'Umar and throw impurities on it—may Allah make them ugly—then this is undoubtedly misguidance. As for the one who leaves it off out of forgetfulness, or because the time did not allow, then this does not indicate evil. Yes.