It is narrated from Sayyiduna Khalid bin Adi al-Juhani (may Allah be pleased with him); he said: I heard the Messenger of Allah (peace and blessings be upon him) say: "Whoever receives a kindness from his brother without asking and without hoping for it, let him accept it and not return it, for it is provision that Allah has sent to him."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 4109