The Messenger of Allah ﷺ said, "Whoever relieves a believer of a hardship from the hardships of this world, Allah will relieve him of a hardship from the hardships of the Day of Resurrection. Whoever eases the burden of one in difficulty, Allah will ease his burden in this world and the next. Whoever conceals the faults of a Muslim, Allah will conceal his faults in this world and the next. Allah continues to aid His servant so long as the servant continues to aid his brother."
قال رسول الله ﷺ: من نفس عن مؤمن كربة من كرب الدنيا، نفس الله عنه كربة من كرب يوم القيامة، ومن يسر على معسر، يسر الله عليه في الدنيا والآخرة، ومن ستر مسلما، ستره الله في الدنيا والآخرة، والله في عون العبد ما كان العبد في عون أخيه.
Muslim narrated it in the chapters on remembrance and supplication (2699) through multiple routes from Abu Muawiya, from Amash, from Abu Salih, from Abu Hurairah, who mentioned it.