It is narrated from Sayyiduna Anas bin Malik, may Allah be pleased with him, that the Messenger of Allah, peace and blessings be upon him, established a pact between the Muhajirun and the Ansar in our house. So it was said to him, "Did the Messenger of Allah, peace and blessings be upon him, not himself say that 'There is no alliance in Islam'?" Sayyiduna Anas, may Allah be pleased with him, replied: "The Messenger of Allah, peace and blessings be upon him, established an alliance between the Muhajirun and the Ansar in our house." Imam Sufyan bin ‘Uyaynah, may Allah have mercy on him, says: The scholars have interpreted this alliance as brotherhood (mu’akhat).
Hadith Referenceالسنن المأثورة / باب الجهاد / 622
Hadith Takhrijسنن ابی داؤد، الفرائض، باب في الحلف، رقم: 2926 وقال الالباني: صحیح، مسند احمد: 96/20، رقم: 12658 وقال الارنوؤط حديث صحيح۔