Sahur is a blessing but it is not compulsory

Narrated 'Abdullah:

The Prophet fasted for days continuously;
the people also did the same but it was difficult for them. So, the Prophet forbade them (to fast continuously for more than one day). They slid, "But you fast without break (no food was taken in the evening or in the morning)." The Prophet replied, "I am not like you, for I am provided with food and drink (by Allah)."

حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، حَدَّثَنَا جُوَيْرِيَةُ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ ـ رضى الله عنه ـ أَنَّ النَّبِيَّ ﷺ وَاصَلَ فَوَاصَلَ النَّاسُ فَشَقَّ عَلَيْهِمْ، فَنَهَاهُمْ. قَالُوا إِنَّكَ تُوَاصِلُ. قَالَ " لَسْتُ كَهَيْئَتِكُمْ، إِنِّي أَظَلُّ أُطْعَمُ وَأُسْقَى ".