Mishkat al-Masabih 2 Knowledge كتاب العلم 55

وَعَنْ أَبِي الدَّرْدَاءِ قَالَ: سُئِلَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: مَا حَدُّ الْعِلْمِ الَّذِي إِذَا بَلَغَهُ الرَّجُلُ كَانَ فَقِيهًا؟ فَقَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «من حَفِظَ عَلَى أُمَّتِي أَرْبَعِينَ حَدِيثًا فِي أَمْرِ دِينِهَا بَعَثَهُ اللَّهُ فَقِيهًا وَكُنْتُ لَهُ يَوْمَ الْقِيَامَة شافعا وشهيدا»

Abu Darda’ told how God’s messenger, when asked how much a man had to learn to become a faqih , replied, “ If anyone preserves for my people forty traditions concerning their religion, God will raise him up in the next world as a faqih , and I shall be an intercessor and witness for him on the day of resurrection.”