It was narrated that Mutarrif said:"I entered upon 'Uthman bin Abi Al-As and he called for milk. I said: I am fasting; He said: "I heard the Messenger of Allah say: 'Fasting is a shield like the of any one of you in battle."' Abu Hurairah said: "The Messenger of Allah said: 'Fasting is a shield."' (Sahih)