An idiom meaning that giving advice or warnings is wasted because the listener pays no attention (like chanting prayers into a horse's ear).
彼に何度注意しても、馬の耳に念仏だ。
No matter how many times I warn him, it's like preaching to the deaf.
そんな理屈を説明しても子どもには馬の耳に念仏だよ。
Explaining that reasoning to children is pointless—they won't understand.
会議で何度言っても、上司には馬の耳に念仏だった。
No matter how many times we said it in the meeting, the boss ignored it.