Ahmad on Sunnah: Not act on hadith until authenticated, understood

Ibn al-Qayyim reported: Abdullah ibn Ahmad said, “I asked my father Ahmad ibn Hanbal about a man who has books, within which are the sayings of the Messenger of Allah, peace and blessings be upon him, and the companions and the followers, but he cannot distinguish weak and rejected narrations, nor a strong chain of narration from a weak one. Is it permissible for him to act upon whatever he wills, to choose from it, to give judgments by it, and to act according to it?” Ahmad, may Allah be pleased with him, said, “He may not act upon it until he asks what may be taken from it, such that he acts upon what is correct. He must ask the scholars about it.”

Source: Iʻlām al-Muwaqqiʻīn 4/158

عن ابن القيم قَالَ عَبْدُ اللَّهِ بْنُ أَحْمَدَ سَأَلْتُ أَبِي عَنْ الرَّجُلِ يَكُونُ عِنْدَهُ الْكُتُبُ الْمُصَنَّفَةُ فِيهَا قَوْلُ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَالصَّحَابَةِ وَالتَّابِعِينَ وَلَيْسَ لِلرَّجُلِ بَصَرٌ بِالْحَدِيثِ الضَّعِيفِ الْمَتْرُوكِ وَلَا الْإِسْنَادِ الْقَوِيِّ مِنْ الضَّعِيفِ فَيَجُوزُ أَنْ يَعْمَلَ بِمَا شَاءَ وَيَتَخَيَّرُ مِنْهَا فَيُفْتِي بِهِ وَيَعْمَلُ بِهِ قَالَ رضي الله عنه لَا يَعْمَلُ حَتَّى يَسْأَلَ مَا يُؤْخَذُ بِهِ مِنْهَا فَيَكُونُ يَعْمَلُ عَلَى أَمْرٍ صَحِيحٍ يَسْأَلُ عَنْ ذَلِكَ أَهْلَ الْعِلْمِ

4/158 إعلام الموقعين عن رب العالمين تغيير الفتوى واختلافها الشريعة مبنية على مصالح العباد