Mujahid (may Allah have mercy on him) says regarding the verse of Allah, the Exalted: ﴿حَتَّىٰيَتَبَيَّنَلَكُمُالْخَيْطُالْأَبْيَضُمِنَالْخَيْطِالْأَسْوَدِ﴾: When a person eats suhoor and thinks that it is still night while in fact the time of Fajr has passed, he should complete his fast, because Allah, the Exalted, has said: ﴿وَكُلُواوَاشْرَبُواحَتَّىٰيَتَبَيَّنَلَكُمُ﴾. And if he eats thinking that the sun has set, but in reality the sun has not set, then he should make up his fast, because Allah, the Exalted, has said: ﴿ثُمَّأَتِمُّواالصِّيَامَإِلَىاللَّيْلِ﴾.
Hadith Referenceسنن سعید بن منصور / كتاب التفسير / 278
Hadith Gradingمحدثین:سنده صحيح، وانظر الكلام عن رواية ابْنِ أَبِي نَجِيحٍ عَنْ مُجَاهِدٍ في الحديث رقم [١٨٤] .
Hadith Takhrij«أخرجه سعيد بن منصور فى (سننه) برقم: 278، وابن أبى شيبة فى (مصنفه) برقم: 9132، 9142»