Bakhair is the word for being well, good, in safety, peace upon. It is linked to the word khairiyat or bakhairiyat (safety).
Subah bakhair is the greeting for Good Morning, which wishes the recipient goodness and safety.
Similarly, Shab-bakhair says Good Night (shab means night).
urduwallahs 
khair means well… khair-iyat means wellness and ba-khair means with wellness. Ba is the prefix which is frequently used in urdu like ba-wazu, ba-jamat, ba-hisab. :)