Full Sharh — Bulugh al-Maram 765
وَعَنْ عَائِشَةَ رَضِيَ اَللَّهُ عَنْهَا قَالَتْ: { دَخَلَ عَلَيَّ اَلنَّبِيُّ - صلى الله عليه وسلم -ذَاتَ يَوْمٍ. فَقَالَ: " هَلْ عِنْدَكُمْ شَيْءٌ? " قُلْنَا: لَا. قَالَ: " فَإِنِّي إِذًا صَائِمٌ " ثُمَّ أَتَانَا يَوْمًا آخَرَ, فَقُلْنَا: أُهْدِيَ لَنَا حَيْسٌ, فَقَالَ: " أَرِينِيهِ, فَلَقَدْ أَصْبَحْتُ صَائِمًا " فَأَكَلَ } رَوَاهُ مُسْلِمٌ 1 .1 - صحيح. رواه مسلم ( 1154 ) ( 170 ).
English Translation
'A’isha (RAA) narrated, ‘One day the Messenger of Allah (ﷺ) entered my house and said, “ls there anything here (to eat)?" I said, ‘NO,’ He said, “I shall then be fasting (today)." Then he came to us another day and we said to him, 'Someone has offered us some hais as a gift.’ He then said, "Show it to me. I had been fasting since this morning, “and he ate from it ( as it was a voluntary fast and not during the obligatory fasting of Ramadan). Related by Muslim.
Source
Bulugh al-Maram(بلوغ المرام)
Fasting
Hadith Number
765