Dictionary / Vocabulary / 何の気なしに
なんのきなしに
unintentionally; inadvertently; calmly; casually
Also written 何の気無しに、なんの気なしに
なんの気なしに言っただけで、別に悪気があってのことではありません。
I just said so without thinking much about it. I didn't mean anything serious.