What is the ruling on a son kissing his parents' hands and placing them on his forehead after the kiss, and is this considered prostration to other than God, taking into account what has been said regarding its permissibility due to the absence of a Sharia impediment, or its prohibition because it resembles prostration?

Kissing the hands of one's parents is permissible. However, placing the hands on the forehead after kissing them is prohibited, as it is not mentioned in the Sunnah (definition) or the narrations (athar), and because it resembles prostration (sujud (definition)), which could even lead to shirk (definition) (polytheism). Scholars have forbidden it and called it the "minor prostration."