Chapter on Fasting with Authorization
Man Lā Yaḥḍuruh al-Faqīh|Volume 2|Book 2|Chapter 31
رَوَى اَلْفُضَيْلُ بْنُ يَسَارٍ عَنْ أَبِي جَعْفَرٍ عَلَيْهِ اَلسَّلاَمُ قَالَ رَسُولُ اَللَّهِ صَلَّى اَللَّهُ عَلَيْهِ وَ آلِهِ: «إِذَا دَخَلَ رَجُلٌ بَلْدَةً فَهُوَ ضَيْفٌ عَلَى مَنْ بِهَا مِنْ أَهْلِ دِينِهِ حَتَّى يَرْحَلَ عَنْهُمْ وَ لاَ يَنْبَغِي لِلضَّيْفِ أَنْ يَصُومَ إِلاَّ بِإِذْنِهِمْ لِئَلاَّ يَعْمَلُوا شَيْئاً فَيَفْسُدَ وَ لاَ يَنْبَغِي لَهُمْ أَنْ يَصُومُوا إِلاَّ بِإِذْنِ اَلضَّيْفِ لِئَلاَّ يَحْتَشِمَهُمْ وَ يَشْتَهِي فَيَتْرُكُهُ لَهُمْ.
It is narrated by al-Fudhayl ibn Yasar from Abu Ja’far عليه السلام that the Messenger of Allah سبحانه وتعالى (peace be upon him and his family) said: "When a man enters a town, he is a guest of those among its people who share his faith until he departs. It is not appropriate for the guest to fast without their permission so that they do not prepare something and it goes to waste. Nor is it appropriate for them to fast without the guest's permission so that he does not feel constrained and refrain from what he desires for their sake."
- Ṣaḥīḥ al-Faqīh