عَنْ أَبِي سَعِيدٍ رَضِيَ اللّهُ عَنْهُ قَالَ: قَالَ رَسُولُ اللّهِ صَلّى اللّهُ عَلَيْهِ وَسَلَّمَ: «مَا مِنْ عَبْدٍ يَصُومُ يَوْمًا فِي سَبِيلِ اللّهِ إلَّا بَاعَدَ اللّهُ بِذَلِكَ الْيَوْمِ وَجْهَهُ عَنِ النَّارِ سَبْعِينَ خَرْيفًا» مُتَّفَقٌ عَلَيْهِ.
Abu Sa'id (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) said: "There is no servant who fasts a day in the path of Allah but that, by that day, Allah distances his face from the Fire by seventy autumns." Agreed upon (al-Bukhari and Muslim).
الدروس · lessons
إنّما ذكر هذا الحديث في باب الجهاد لعموم مدلول عبارة "في سبيل الله تعالى" بما يشمل الجهاد وغيره من الطاعات. فيكون المعنى: مجاهدة النفس على صيامِ يومٍ تطوعًا، وتحمُّل مشقة الصيام في سبيل اللّهِ ابتغاء مرضاته ورجاء ثوابه.
This hadith was mentioned in the chapter on jihad only because of the generality of the meaning of the phrase "in the path of Allah the Exalted," which encompasses jihad and other acts of obedience. So the meaning is: struggling against one's soul to fast a day voluntarily, and bearing the hardship of fasting in the path of Allah, seeking His pleasure and hoping for His reward.