What is the Sharīʿah's ruling on a sister's refusal to host her husband's father in his current state (he does not pray, does not bathe, and does not change his clothes), given her fear that she might cause her husband to be undutiful to his father, and how can this situation be handled without falling into God's disobedience by being undutiful to a parent?

Kindness to parents is obligatory for children, whether the parent is obedient or disobedient, Muslim or disbeliever, as long as it is within the bounds of obedience to Allah, due to the generality of His saying, the Exalted: "And We have enjoined upon man, to his parents, good treatment." The husband's father is considered among the most confirmed and rightful neighbors for a woman, as stated in His saying, the Exalted: "Worship Allah and associate nothing with Him, and to parents do good, and to relatives, orphans, the needy, the neighbor at hand, and the distant neighbor." Children and neighbors must strive for the guidance of their parents and neighbors, advising them with wisdom and good admonition, frequently supplicating for them, being patient in this, and seeking help from those whose words have influence among their contemporaries or scholars, or through means such as beneficial tapes and books.

When the father does not listen, children can maintain a daily lesson at home where they read in the father's presence from hadiths of encouragement and discouragement. Recommended books include: Riyadh as-Salihin, Sahih at-Targhib wat-Tarhib, and Al-Matjar ar-Rabih fi Thawab al-Amal as-Salih. It is not necessary for the son's wife to sit with her father-in-law; rather, she should honor him with what is available, such as providing food and shelter, and encourage her husband to show filial piety and kindness to him.