Ruling on kissing one’s wife’s mother

What is the Islamic ruling on greeting and kissing one’s wife’s mother on her cheek or neck? Please quote evidence from the Qur’aan and Sunnah.

Praise be to Allaah.  

It is permissible for her to uncover her face, and there is no scholarly dispute on this point. But with regard to kissing her, it is not permissible to kiss her on the mouth because there is the danger that this may provoke desire. But if he kisses her on the head or forehead out of respect towards her when returning from travel etc., and there is no risk of that provoking desire, then it is o.k. And Allaah knows best.