Al-Suyuti reported: The judge Abu Sa’id responded comprehensively in regard to a question about the school of Al-Shafi’i with four rules (qawa’id); first, certainty does not remove doubt. The basis of this is the saying of the Prophet, peace and blessings be upon him, “Verily, Satan comes to one of you while he is in prayer and he says to him: you have lost your ablution; so do let him not leave unless he hears a sound or finds an odor.” Second, hardship leads to ease, and the basis of this is the saying of the Almighty, “We have not placed upon you hardship in religion,” (22:78) and the saying of the Prophet, “I was sent with the upright, lenient religion.” Third, harm should be removed, and the basis of this is the saying of the Prophet, “There is no harming, nor harming others.” Fourth, customs are a basis of judgment, because of the saying of the Prophet, “What the Muslims view as good is regarded by Allah as good.” Thus, he ended his letter. Other scholars said that these four rules are the pillars of juristic understanding (al-fiqh) and the entirety of doctrine, and some of them added to it a fifth rule, which is that matters are according to their objectives (al-maqasid), because of the saying of the Prophet, “Deeds are according to intentions,” and he said, “Islam is built upon five pillars,” and likewise jurisprudence is based upon five rules.
Source: al-Ashbāh wal-Naẓāʼir 1/7-8
عن السيوطي قَالَ الْقَاضِي أَبُو سَعِيدٍ فَلَمَّا بَلَغَ الْقَاضِي حُسَيْنًا ذَلِكَ رَدَّ جَمِيع مَذْهَب الشَّافِعِيِّ إلَى أَرْبَع قَوَاعِد الْأُولَى الْيَقِين لَا يُزَال بِالشَّكِّ وَأَصْل ذَلِكَ قَوْله صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إنَّ الشَّيْطَانَ لَيَأْتِي أَحَدَكُمْ وَهُوَ فِي صَلَاته فَيَقُولُ لَهُ أَحْدَثْتَ فَلَا يَنْصَرِفْ حَتَّى يَسْمَعَ صَوْتًا أَوْ يَجِدَ رِيحًا وَالثَّانِيَة الْمَشَقَّة تَجْلِب التَّيْسِير قَالَ تَعَالَى وَمَا جَعَلَ عَلَيْكُمْ فِي الدِّينِ مِنْ حَرَجٍ وَقَالَ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ بُعِثْتُ بِالْحَنِيفِيَّةِ السَّمْحَةِ الثَّالِثَة الضَّرَر يُزَال وَأَصْلُهَا قَوْله صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ لَا ضَرَرَ وَلَا ضِرَارَ الرَّابِعَة الْعَادَة مُحَكَّمَةٌ لِقَوْلِهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ مَا رَآهُ الْمُسْلِمُونَ حَسَنًا فَهُوَ عِنْدَ اللَّهِ حَسَنٌ انْتَهَى قَالَ بَعْض الْمُتَأَخِّرِينَ فِي كَوْن هَذِهِ الْأَرْبَع دَعَائِم الْفِقْه كُلّه نَظَر فَإِنَّ غَالِبه لَا يَرْجِع إلَيْهَا إلَّا بِوَاسِطَةِ وَتَكَلُّف وَضَمّ بَعْض الْفُضَلَاء إلَى هَذِهِ قَاعِدَة خَامِسَة وَهِيَ الْأُمُور بِمَقَاصِدِهَا لِقَوْلِهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إنَّمَا الْأَعْمَالُ بِالنِّيَّاتِ وَقَالَ بُنِيَ الْإِسْلَامُ عَلَى خَمْسٍ وَالْفِقْه عَلَى خَمْس
1/7-8 الأشباه والنظائر للسيوطي كتاب الأول في شرح القواعد الخمس التي ترجع إليها جميع مسائل الفقه