If the fasting Person drank after the Athan of Fajr

Question :

If the fasting person drank after he heard the Athan of Fajr, is his fasting correct (i.e., acceptable)?

Answer:

If the fasting person drank after he heard the Athan of Fajr, if the person who calls the Athan does so after it becomes clear to him that it is morning, then it is not permissible for the fasting person to eat or drink after it. If the person who calls the Athan does so before it becomes clear to him that it is morning (dawn), then there is no harm in eating and drinking until it becomes clear that it is morning (dawn). This is due to Allâh's Statement:
"So, now touch them (i.c., have sexual relations with women) and seek that which Allah has written for you. And eat and drink until the white thread (of dawn) becomes distinct to you from the black thread. "

Also, the Prophet said:
"Verily, Bilal calls the Athan at night, so eat and drink until you hear the Athan of Ibn Umm Maktum. For verily, he does not call the Athan until Fajr time commences."

For this reason it is necessary for those who call the Athan to strive to be exact in the Athan of the morning (i.e., dawn). They should not call the Athan until it becomes clear to them that it is morning or they are certain of its entrance by exact clocks. This is so that they do not deceive the people and forbid them from what Allâh has allowed for them, and allow the morning prayer for them before its time. For this contains a serious danger.

Source:
Ash-Shaykh Ibn 'Uthaimin
Fatawa Islamiyah, Vol. 3 Pages 253-254