Praise be to Allaah.
It is mustahabb to kiss the hands of righteous people and the greatest scholars, and it is makrooh to kiss the hand of anyone else. The hand of the beardless man should not be kissed under any circumstances,
(From Fatawa al-Imaam al-Nawawi, p. 71)
In the commentary on the book, it says:
If a person wants to kiss another person's hand, if this is because of his asceticism, righteousness, knowledge, position or modesty, or other reason that has to do with his commitment to religion, then it is not makrooh. In such cases it is mustahabb, because Abu ‘Ubaydah kissed the hand of ‘Umar (may Allaah be pleased with them both).
But if it is because of the person’s riches, wealth, high rank or status in the eyes of the people of this world, and so on, then it is intensely makrooh.
Al-Mutawalli, one of our companions, said: It is not permitted, and he indicated that it is haraam.
It was narrated in Sunan Abi Dawood that Zaari’ (may Allaah be pleased with him), who was among the delegation of ‘Abd Qays, said: “We started to get out from our howdahs and we kissed the hands and feet of the Prophet (peace and blessings of Allaah be upon him).