In the name of Allah,
The Malikis say that if you’re not sure it’s dawn, don’t eat. It was permitted by Shaafi, Ibn Hanbal, and Abu Haneefah.
Scholars dispute whether the individual should make up the fast. A group of Salaf and Ibn Taymiyyah[i] and Ibn `Uthaymin say his fast is legitimate and does not need to be made up. The four schools of law agree he must make it up.
Abd al-Razzaaq said that Ibn ‘Abbaas (may Allaah be pleased with him) said, “Allaah has permitted you to eat and drink so long as there is any uncertainty in your mind.”[ii]
Allah has clearly stated when one should start their daily fast. “Eat and drink till the white thread of the dawn becomes discernible from the black thread [of the night],” [iii]
Abu Dawud cited Ahmad ibn Hanbal: “If you have some uncertainty regarding fajr, eat till you are sure dawn has come.”
Ibn ‘Abbas, ‘Ata, al’Auza’i, and Ahmad agree. According to An-Nawawi, “ash-followers Shafai’s believe that one can eat if he isn’t sure if dawn has come or not.”[iv]
Peace and blessings be upon the last and final prophet.
Sources:
[i] Fath al-Baari, 4/135; this is also the opinion of Shaykh al-Islam Ibn Taymiyyah, Majmoo’ al-Fataawa, 29/263).
[ii] Rulings pertaining to Ramadan, A Collection of Works by Sheikh Muhammad Salih Al-Munajjid, Islamfuture, page 56
[iii] al-Baqarah 2:187
[iv] Fiqh us sunnah, Sayed Sabiq, Chapter Fasting, Page 258