It is narrated from Sayyiduna Dumayrah bin Abi Dumayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever does not show mercy to our young and does not recognise the right of our elders is not one of us; and whoever deceives us is not one of us; and a believer is not a believer until he loves for his believing brothers what he loves for himself."
Hadith Referenceالمعجم الكبير للطبراني / باب الضاد / 8123