Man Lā Yaḥḍuruh al-Faqīh
Hadith 4322002 - وَ سَأَلَهُ سَمَاعَةُ : عَنْ قَوْلِهِ اَلصَّائِمُ بِالْخِيَارِ إِلَى زَوَالِ اَلشَّمْسِ قَالَ «إِنَّ ذَلِكَ فِي اَلْفَرِيضَةِ فَأَمَّا فِي اَلنَّافِلَةِ فَلَهُ أَنْ يُفْطِرَ أَيَّ سَاعَةٍ شَاءَ إِلَى غُرُوبِ اَلشَّمْسِ».
Hadith.2002 - Sama‘ah asked Abu ‘Abd Allah (as) about the statement: "The fasting person has the option until the sun passes its zenith."
Imam (as) replied: "That applies to obligatory fasts. As for voluntary fasts, one may break the fast at any time they wish until sunset."