Sayyiduna Ali (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "The protection granted by all the Muslims is the same; even the lowest of them may grant protection. Whoever violates the protection granted by a Muslim, upon him is the curse of Allah, the angels and all the people; neither his obligatory nor his voluntary deeds will be accepted. And whoever takes a believer as his patron without the permission of his own patrons, upon him is the curse of Allah, the angels and all the people; neither his obligatory nor his voluntary deeds will be accepted." (b) Sayyiduna Ali (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him): "The blood of all the believers is equal; they are united like one hand against those opposed to them, and even the lowest of them may grant protection."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18168