The Prophet ﷺ said, "Fasting is a shield."
عن النبي ﷺ قال: الصوم جنة.
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Tirmidhi (2616), Ibn Majah (3973), and Ahmad (22016) all narrated it from the hadith of Maamar, from Asim bin Abu Najud, from Abu Waail, from Muaz bin Jabal, who mentioned it in a long hadith. Tirmidhi said, hasan sahih. I say, Abu Waail, who is Shaqiq bin Salama, did not hear from Muaz.Ahmad (22133) narrated it through Hammad bin Salama, from Asim, from Shahr bin Hawshab, from Muaz, who mentioned it. There is well-known discussion about Shahr bin Hawshab, and he too did not hear from Muaz. Nasai (2225, 2226) and Ahmad (22032, 22051, 22047) both narrated it through other routes from Muaz bin Jabal, who mentioned it in both a long and a shortened version. Taking all these routes together, along with the established foundations mentioned before, this hadith becomes hasan.On this subject there is also a report from Abu Ubayda, attributed to the Prophet ﷺ, "Fasting is a shield, as long as one does not tear it." This was narrated by Nasai (2233), Darimi (1773), Bukhari in Tarikh al-Kabir (21/7), Ahmad (1690), Abu Yaala (878), and Ibn Khuzayma (1892), all from the hadith of Wasil, freedman of Abu Uyayna, from Bashar bin Abu Sayf Jarmi, from Walid bin Abdul-Rahman Jurashi, from Iyad bin Ghatif, from Abu Ubayda bin Jarra, who mentioned it in a long hadith, though some abridged it. Bashar bin Abu Sayf was only deemed reliable by Ibn Hibban, and so Ibn Hajar said of him, "Acceptable," meaning when corroborated.I say, Masaar did corroborate him from Walid, except that Walid said, "Our companions narrated to us from Abu Ubayda, who said, 'Fasting is a shield, as long as one does not tear it.'" This was narrated by Nasai (2235), and in it Walid bin Abdul-Rahman did not name his companions, and Abu Ubayda did not attribute it to the Prophet. As for his statement, "as long as one does not tear it," Darimi said this means through backbiting.On this subject there is also what was reported from Anas, that the Messenger of Allah said, "Envy consumes good deeds as fire consumes firewood, charity extinguishes sin as water extinguishes fire, prayer is the light of the believer, and fasting is a shield from the fire." This was narrated by Ibn Majah (4210) from Harun bin Abdullah Hammal and Ahmad bin Azhar, who both said, Ibn Abu Fudayk narrated to us, from Isa bin Abu Isa Hannat, from Abu Zinad, from Anas, who mentioned it. Abu Yaala (3656) narrated it from Harun bin Abdullah alone. Its chain is extremely daif, for Isa Hannat, who is Ibn Abu Isa Maysara Ghifari Madani, is daif by consensus of the scholars, to the point that Abu Dawud, Daraqutni, and others said, "His hadith is to be abandoned."