If one eats after the dawn has appeared, his fast is invalid
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Question: If a Muslim continues eating during the pre-dawn meal until the dawn appears, and he does not know whether he must abstain and continue fasting that day, remaining in a state of fasting, or whether he must make up the day? May Allah reward you with good.
Answer: It is obligatory for a Muslim who is fasting an obligatory fast to abstain from eating when the dawn appears. If he eats or drinks after the dawn has appeared, his fast is invalid, and it becomes obligatory for him to make it up; based on the saying of Allah, the Exalted: [Surat al-Baqarah: 187].
Answer: It is obligatory for a Muslim who is fasting an obligatory fast to abstain from eating when the dawn appears. If he eats or drinks after the dawn has appeared, his fast is invalid, and it becomes obligatory for him to make it up; based on the saying of Allah, the Exalted:
And eat and drink until the white thread of dawn becomes distinct to you from the black thread [of night]. Then complete the fast until the sunset.
وَكُلُواْ وَاشْرَبُواْ حَتَّى يَتَبَيَّنَ لَكُمُ الْخَيْطُ الأَبْيَضُ مِنَ الْخَيْطِ الأَسْوَدِ مِنَ الْفَجْرِ ثُمَّ أَتِمُّواْ الصِّيَامَ إِلَى الَّليْلِ
Source
binbaz.org.sa
The Arabic text is copied verbatim from the original source, without any edits.