Mujahid (may Allah have mercy on him) says regarding the verse of Allah, the Exalted: ﴿حَتَّىٰ يَتَبَيَّنَ لَكُمُ الْخَيْطُ الْأَبْيَضُ مِنَ الْخَيْطِ الْأَسْوَدِ﴾: 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: ﴿وَكُلُوا وَاشْرَبُوا حَتَّىٰ يَتَبَيَّنَ لَكُمُ﴾. 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: ﴿ثُمَّ أَتِمُّوا الصِّيَامَ إِلَى اللَّيْلِ﴾.