the goodness of (someone's) heart

Translations
по доброте (чьей-то) души
She helped him out of the goodness of her heart.
Она помогла ему по доброте своей души.
Definitions
A phrase used to describe someone's genuine kindness, generosity, or compassion, implying that their good actions are motivated by sincere feelings rather than obligation or personal gain.
Words
heart

noun
сердце
goodness

noun
доброта