Musnad Ahmad 459:5

Al-Walid ibn Muslim narrated to us, Thawr ibn Yazid narrated to us, Khalid ibn Ma'dan narrated to us, he said: Abd al-Rahman ibn Amr al-Sulami and Hujr ibn Hujr narrated to us, they said: We came to al-Irbad ibn Sariyah, and he was among those about whom it was revealed: "Nor [is there blame] on those who, when they came to you that you might give them mounts, you said, 'I can find nothing for you to ride upon'" [At-Tawbah: 92]. We greeted him and said: We have come to you as visitors, as those inquiring after your health, and as seekers of knowledge. Al-Irbad said: The Messenger of Allah (peace and blessings of Allah be upon him) led us in the morning prayer one day, then he turned to us and delivered an eloquent sermon that caused eyes to shed tears and hearts to tremble. A man said: O Messenger of Allah, it is as if this is the sermon of one bidding farewell, so what do you enjoin upon us? He said: "I enjoin you to fear Allah (taqwa), and to listen and obey, even if [your leader] is an Abyssinian slave. For whoever among you lives after me will see much disagreement. So you must follow my Sunnah and the Sunnah of the rightly-guided, guided successors; hold fast to it and bite onto it with your molar teeth. And beware of newly invented matters, for every newly invented matter is an innovation (bid'ah), and every innovation is a misguidance."