The words of the Prophet (peace and blessings of Allaah be upon him) – “fasting is a shield” – means that it is something that screens and protects you from what you fear.

It protects you from falling into sin which is the cause of punishment. He (peace and blessings of Allaah be upon him) said: “Fasting is a shield against the Fire like the shield of any one of you in battle.”

See authentic hadith below:

Abu Ubaydah( radiyallahu anhu) had once reported to have said “I have heard the holy prophet of Islam, Mohamed (Peace be upon him) saying: Fasting is a protective shield for man , as long as he does not tear up that protection.”

Note: “Protective Shield” here means : just as a man Protects himself fasting protect him with a shield, similarly Fasting Protects him from  his well -known enemy shytan[satan].

It is advised that a person who is fasting should avoid obscene speech and should not behave foolishly and ignorantly, and if somebody fights with him or insults him, he should tell him twice, ‘I am fasting. See proof below :

Once somebody inquired from the holy prophet of Islam, ” What causes the fast to be torn?” He replied: ” Telling lies and backbiting. This Hadith, when read along with many others, actually tells us to avoid such actions which causes fasting to be wasted.