out of the goodness of heart
out the goodness of (one's) heart
Because of one's altruistic generosity or goodwill, without personal or ulterior motivations. You expect me to believe you would do this out of the goodness of your heart? Come on, what are you looking for in return?
*out of the goodness of one's heart
Fig. simply because one is kind. (*Typically: be something ~; do something ~.) What are you going to pay me? You don't expect me to do this out of the goodness of my heart, do you?