What is the ruling on obeying parents if they ask their child to do something that helps them commit a sin, given that the parents will become angry and curse the child if he refuses, and is it permissible for the son to resort to dissimulation (tawriyah) or stratagem to avoid the sin in such cases?

The rights of parents are great, and obedience to them is obligatory in what is permissible. However, there is no obedience to them if they command what contradicts the Sharia, and it is not permissible for the child to assist them in disobedience. What the child believes to be forbidden, he must not help his parents with it. However, he must be gentle and deal with them with wisdom and tact, using allusions and subtle hints, advising them, and explaining the ruling of the Sharia to them with politeness and gentleness.