Is it permissible to kiss the face, hand, and foot of one's parents? Is this act considered polytheism (shirk)? And is doubt (shakk) condemned in Islam in the same way as conjecture (dhann)?

The narrations regarding the permissibility of kissing the hand and foot are well-established. The general principle concerning the actions of the Messenger of Allah, peace and blessings be upon him, is that they are not exclusive to him unless there is evidence to the contrary. The actions of the Salaf indicate non-exclusivity. The legitimacy of kissing is for people of virtue, such as the righteous and parents, and not for everyone whose obedience is obligatory. Doubt is absolutely condemned in matters of belief because nothing benefits except certainty. Suspicion (al-ẓann) in the Quran refers to corrupt belief, but doubt (al-shakk) in its conventional logical sense, such as perceiving a thing with an equal probability of its opposite, can be half of knowledge. A Muslim is advised to seek beneficial knowledge, righteous deeds, and gradual progression in acquiring knowledge.