I was given a Christmas song quiz to do by some one i am now stuck just two songs can anyone help me please

There are letters to one line of the song(s), and i was wondering if anyone on her could help please

FTCMPRPPP OR WAMLHBIAMFIB
Does anyone know the line to those please

FTCMPRPPP is surely something from Little Drummer Boy, going by 'pa rum pum pum pum' at the end.

I can tel youl it is not from the little drummer boy, i seen the Lyrics