Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
darimi:165Muslim b. Ibrāhīm > Abū ʿAqīl > Saʿīd al-Jurayrī > Abū Naḍrah

[Machine] When Abu Salamah arrived in Basrah, both Hassan and I went to visit him. He said to Hassan, "Are you Hassan? No one in Basrah is dearer to me for a meeting than you. This is because I heard that you give fatwas based on your opinion, but do not give fatwas based on your opinion unless it is a Sunnah from the Messenger of Allah ﷺ or a revealed book."  

الدارمي:١٦٥حَدَّثَنَا مُسْلِمُ بْنُ إِبْرَاهِيمَ حَدَّثَنَا أَبُو عَقِيلٍ حَدَّثَنَا سَعِيدٌ الْجُرَيْرِيُّ عَنْ أَبِي نَضْرَةَ قَالَ

لَمَّا قَدِمَ أَبُو سَلَمَةَ الْبَصْرَةَ أَتَيْتُهُ أَنَا وَالْحَسَنُ فَقَالَ لِلْحَسَنِ أَنْتَ الْحَسَنُ؟ «مَا كَانَ أَحَدٌ بِالْبَصْرَةِ أَحَبَّ إِلَيَّ لِقَاءً مِنْكَ وَذَلِكَ أَنَّهُ بَلَغَنِي أَنَّكَ تُفْتِي بِرَأْيِكَ فَلَا تُفْتِ بِرَأْيِكَ إِلَّا أَنْ تَكُونَ سُنَّةٌ عَنْ رَسُولِ اللَّهِ ﷺ أَوْ كِتَابٌ مُنْزَلٌ»