Sayyiduna al-Irbad bin Sariyah (may Allah be pleased with him) related that one day the Messenger of Allah (peace and blessings be upon him) gave an eloquent sermon by which eyes shed tears and hearts became fearful. A man from among the Muslims said: "O Messenger of Allah, it is as if this is the sermon of one bidding farewell; so what covenant do you take from us?" He (peace and blessings be upon him) said: "I have left you upon a white (shining) path whose night is like its day; after me none of you will deviate from it except one who is destroyed. Whoever of you lives will see much disagreement, so beware of innovations, and hold fast to my Sunnah and the Sunnah of the Rightly Guided Caliphs; bite onto it firmly with your molars. And hold fast to hearing and obeying, even if it be an Abyssinian slave."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 15733