Umar ibn al-Khattaab, rahimahullaah, said:
“There is no excuse for anyone going astray thinking that he is upon guidance. Nor for abandoning guidance thinking it to be misguidance, since the affairs have been made clear, the proof established  and the excuse cut off.”
That is because the Sunnah and the Jamaa’ah have consolidated and safeguarded all of the Religion. It has been made clear to the people, so it is upon the people to comply and follow.
1. Al-‘Irbaad ibn Saariyah, radiallaahu’anhu, reports that the Prophet said, “…. I have left you upon clear guidance. Its night is like its day. No one deviates from it after me except that he is destroyed.” Reported by Ahmad, Ibn Maajah (no. 43) and al-Haakim. It is declared saheeh by Shaikh al-Albaanee in as-Saheehah (no. 937).
2. Reported by Ibn Battah in, al-lbaantul-Kubraa (no. 162) by way of Awzaa’ee that it reached him that ‘Umar ibn al-Khattaab said it. However, its chain is munqati’ (disconnected).
Al-Marwazee reports in as-Sunnah (no. 95) that ‘Umar ibn ‘Abd Allah-‘Azeez said, “There is no excuse for anyone, after the Sunnah, to be misguided upon error which he thought was guidance.“
3.’Abdullaah ibn Mas’ood radiallaahu ‘anhu, said,
“Follow and do not innovate, for you have been given that which is sufficient and every innovation is misguidance.“
Reported by Abu Khaithamah in Kitaab Ul-‘Ilm (no. 540) and declared saheeh by Shaikh al-Albaanee.
Kitaab Sharh us-Sunnah by Al-Barbahaaree.