Whoever fasts one day in the cause of Allah, Allah shall put between him and Hellfire a trench as wide as the distance between the heavens and the earth
Good hadithعن أبي أمامة رضي الله عنه مرفوعاً: «من صام يوماً في سبيل الله جعل الله بينه وبين النار خَنْدَقًا كما بين السماء والأرض».
Abu Umāmah (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "Whoever fasts one day in the cause of Allah, Allah shall put between him and Hellfire a trench as wide as the distance between the heavens and the earth."
Explanation
This Hadīth demonstrates the virtue of fasting a day solely for the sake of Allah. The reward for this is that Allah saves the fasting person from Hellfire and keeps him away from it at a distance equal to that between the heavens and the earth.
Source · Narrated by At-Termedhy
From the Hadith Encyclopedia (hadeethenc.com).