Mishkat al-Masabih 7 Fasting كتاب الصوم 104

وَعَن مُسلم الْقرشِي قَالَ: سَأَلت أَوْ سُئِلَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ عَن صِيَام الدَّهْر فَقَالَ: «إِنَّ لِأَهْلِكَ عَلَيْكَ حَقًّا صُمْ رَمَضَانَ وَالَّذِي يَلِيهِ وَكُلَّ أَرْبِعَاءَ وَخَمِيسٍ فَإِذًا أَنْتَ قَدْ صُمْتَ الدَّهْرَ كُلَّهُ» . رَوَاهُ أَبُو دَاوُدَ وَالتِّرْمِذِيُّ

Muslim al-Qurashi said that he or someone else asked God’s messenger about perpetual fasting, and he replied, “You have a duty to your family. Fast during Ramadan and the following month, and every Wednesday and Thursday. You will then have observed a perpetual fast.” Abu Dawud and Tirmidhi transmitted it.