Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: The Messenger of Allah (peace and blessings be upon him) said: "Allah, the Mighty and Majestic, has supported me with the strongest of the Arabs in tongues and arms - Banu Qaylah, that is, the Aws and the Khazraj."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11964