Sehar timing: Sahih al-Bukhari 617

Narrated Salim bin `Abdullah:

My father said that Allah s Apostle said, “Bilal pronounces ‘Adhan at night, so keep on eating and drinking (Suhur) till Ibn Um Maktum pronounces Adhan.” Salim added, “He was a blind man who would not pronounce the Adhan unless he was told that the day had dawned.”

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ سَالِمِ بْنِ عَبْدِ اللَّهِ، عَنْ أَبِيهِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ “‏ إِنَّ بِلاَلاً يُؤَذِّنُ بِلَيْلٍ، فَكُلُوا وَاشْرَبُوا حَتَّى يُنَادِيَ ابْنُ أُمِّ مَكْتُومٍ ‏”‏‏.‏ ثُمَّ قَالَ وَكَانَ رَجُلاً أَعْمَى لاَ يُنَادِي حَتَّى يُقَالَ لَهُ أَصْبَحْتَ أَصْبَحْتَ‏.‏

Reference : Sahih al-Bukhari 617
In-book reference : Book 10, Hadith 15
Web Ref: https://sunnah.com/bukhari/10/15