Sadaqah (charity) is the concept of giving charity voluntarily fi sabillilah فِي سَبِيلِ ٱللَّٰهِ (for the cause of Allah).
Even a smile is Charity
Sadaqah also describes a voluntary charitable act towards another being, whether through generosity, love, compassion or faith. These acts are not necessarily physical or monetary. Simple good deeds such as a smile, or a helping hand, are seen as acts of Sadaqah.