What is the ruling on a wife kissing the hands of her husband's parents?

There is no objection to a wife kissing her husband's father's hand if there is no fear of temptation (fitna), as this is a sign of respect and reverence for an elder. This falls under the category of honoring an elderly Muslim. Some scholars have permitted kissing the hand of a father, mother, elder brother, scholar, or an elderly sheikh out of respect.