Mishkat al-Masabih 11 Business Transactions كتاب البيوع 23

عَنْ عَبْدِ اللَّهِ بْنِ مَسْعُودٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «طَلَبُ كَسْبِ الْحَلَالِ فَرِيضَةٌ بَعْدَ الْفَرِيضَةِ» . رَوَاهُ الْبَيْهَقِيُّ فِي شعب الْإِيمَان

‘Abdallah b. Mas’ud reported God’s Messenger as saying, “Trying to earn a lawful livelihood is an obligatory duty in addition to the duties which are obligatory.” Baihaqi transmitted it in Shu’ab al-iman .