What is the ruling on greeting or saluting by raising the hands or clasping them together, like the greeting of Hindus or Chinese?

If the greeting is by raising the hands without uttering "Salam" while being able to do so, then it is forbidden, due to imitating the disbelievers.

Al-Tirmidhi narrated that the Prophet (peace and blessings be upon him) said: "Do not imitate the Jews and Christians, for the greeting of the Jews is by pointing with the finger, and the greeting of the Christians is with the palms."

Al-Nasa'i narrated from Jabir, elevated to the Prophet: "Do not greet like the Jews, for their greeting is with their heads, palms, and pointing."

Al-Hafiz said in Al-Fath: "The prohibition of greeting by gesturing is specific to one who is able to speak, both physically and legally. Otherwise, it is permissible for one who is occupied in a way that prevents him from uttering the greeting in response; such as one who is praying, or one who is far away, or a mute person, and similarly, greeting a deaf person."

The imitation forbidden by Islamic law is imitating polytheists in what is specific to them, such that anyone who sees it would think that the doer is one of them.