If you want your tefillos to be accepted by Hakadosh Baruch Hu be cautious with your mouth,because that is your utensil for prayer. Be cautious and don’t speak profanely, curses, swears, lashon hara, and the like, because prayer is a gift to Hakadosh Baruch Hu and the mouth is the vessel that holds your gift. The vessel can’t be dirty… If it is, it is a disgrace for the King, and it is a disgrace for the gift… You should speak Torah, tefillah, permitted speech, and nothing else. ~ Kitzur Shlah