The Book of Miscellany
كتاب المقدمات
(29) Chapter: Fulfillment of the needs of the Muslims
(29) - باب قضاء حوائج المسلمين
Riyad as-Salihin 244 
Ibn 'Umar (May Allah bepleased with them) reported:
Messenger of Allah (ﷺ) said, "A Muslim is a brother of (another) Muslim, he neither wrongs him nor does hand him over to one who does him wrong. If anyone fulfills his brother's needs, Allah will fulfill his needs; if one relieves a Muslim of his troubles, Allah will relieve his troubles on the Day of Resurrection; and if anyone covers up a Muslim (his sins), Allah will cover him up (his sins) on the Resurrection Day".

[Al-Bukhari and Muslim].

وعن ابن عمر رضي الله عنهما أن رسول الله صلى الله عليه وسلم قال‏:‏ ‏ "‏المسلم أخو المسلم لا يظلمه ولا يسلمه‏.‏ من كان في حاجة أخيه كان الله في حاجته، ومن فرج عن مسلم كربة فرج الله عنه بها كربة من كرب يوم القيامة، ومن ستر مسلمًا ستره الله يوم القيامة‏"‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏ ‏.‏
Reference : Riyad as-Salihin 244
In-book reference : Introduction, Hadith 244