قال رسول الله صلى الله عليه وسلم

رُبَّ صَاءمٍ لَيسَ لَهُ مِنْ صِياَمِهِ إلَّا الْجُوعُ وَالْعَطَشْ، وَرُبَّ قَاءمٍ لَيسَ لَهُ مِنْ قِيَامِهِ إلَّا السَّهَرُ.

"There may be many fasting persons who has nothing from their fast except hunger and thirst, and there may be many fasting persons who has nothing from their standing in [prayer] except staying up late."

(Narrated by Al-Nasa'i and Ibn Majah)