It is reported that Sufyān b. ‘Uyainah – Allāh have mercy on him – said:
Verily, the Messenger of Allāh ﷺ is the highest standard; things are measured by him: his character, lifestyle and behavior. Whatever agrees with [these] is true and correct, and whatever contradicts [them] is wrong.
Al-Khatīb Al-Baghdādī, Akhlāq Al-Rāwī wa Ādāb Al-Sāmi’ article 8.
Mālik b. Mighwal said:
Al-Sha’bī once said to me, “When these [people] report to you from Allāh’s Messenger – praise and peace of Allāh be upon him, adhere to it; but when they merely opine, throw it in the trash.”
Al-Dārimī, Al-Sunan 1:78.
From whom does Knowledge Come?
It is reported that ‘Abdullāh b. Masʿūd – Allāh be pleased with him – said:
The people will remain upon goodness as long as knowledge comes to them from the Companions of Allāh’s Messenger – Allāh’s praise and peace be upon him, and from their seniors. But when knowledge comes to them from their minors, that is when they will be destroyed.
Ibn ‘Abd Al-Barr, Jāmi’ Bayān Al-‘Ilm wa Fadlihi article 1060.
Being upon a good and right path is based on following the knowledge of the Companions and seniors: scholars and people who adhere to the Sunnah, whereas taking knowledge from minors like ignorants and heretics is a sign of destruction.
Following Hadith Exactly
Abū Ja’far reports:
Whenever Ibn ‘Umar – Allāh be pleased with him – heard a ḥadīth from Allāh’s Messenger – Allāh’s praise and peace be upon him – he never went beyond it, and he never fell short of it.
Ibn Mājah, Al-Sunan, ḥadīth #4. Shaykh Al-Albānī graded this narration ṣaḥīḥ in his edition of the Sunan.
Shaykh Al-Albānī explained that ‘he never went beyond it’ means: he never added anything to what was in the ḥadīth or overstepped the bounds of the ḥadīth; and ‘he never fell short of it’ means: he never neglected what was in the ḥadīth.
Stupid: Asking for Quran without Sunnah
It is reported that ‘Imrān b. Husayn – Allāh be pleased with him – was once relating hadīth amongst a group of people, when a man said:
Leave this and give us something from the Book of Allāh. ‘Imrān said, “You are a dunce (stupid). Do you find in the Book of Allāh details of prayer. Do you find in the Book of Allāh details of fasting!? This Qur`ān prescribes those matters, and the Sunnah explains them.”
Al-Harawī, Dham Al-Kalām article 244, et al with various wordings.