If a woman's husband is dead but his father is alive, is it permissible for the widow to greet her father-in-law?
A father-in-law is a permanent Mahram (spouse or permanently unmarriageable relative) for a woman, because she is the wife of his own son. Therefore, it is permissible for her to greet him, shake hands with him, and show in front of him what she is permitted to show in front of her blood Mahrams. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.