Sayyiduna Abu Ubaidah bin Jarrah (may Allah be pleased with him) said: I heard the Messenger of Allah (peace and blessings of Allah be upon him) say: "Fasting is a shield as long as it is not torn." Imam Darimi (may Allah have mercy on him) said: That is, by backbiting (one should not spoil the fast).
Hadith Takhrijاس روایت کی سند حسن ہے۔ دیکھئے: [نسائي 2232] ، [أبويعلی 878] ، [مجمع الزوائد 3830]
Brief Explanation
(Commentary on Hadith 1769)
The meaning of this hadith is that as long as a person does not engage in backbiting, does not lie, the fast remains a shield for him, because lying, backbiting, and evil deeds create a breach in the fast and the fast becomes spoiled, just as a shield is torn when struck.