strengthen his body
1 One shall intend to strengthen his body through sleeping so that he can worship Allah
Allah made sleep a rest so that one can stand up for performing the prayer. The lack of sleeping results in the inability to worship Allah. Please consider this story
The Messenger of Allah ( may the peace and blessings of Allah be upon him ) made a bond of brotherhood between Salman and Abu Ad-Darda. Salman went to visit Abu Ad-Darda, and saw Umm Ad-Darda wearing shabby clothes, So he said:
'Why are you wearing such shabby clothes?' She said: 'Your brother Abu Ad-Darda has no interest in the world.' So when Abu Ad-Darda arrived, he prepared some food for him (Salman) and said: 'Eat, for I am fasting.' He said: 'I shall not eat until you eat.'" He said: "So he ate. When night came Abu Ad-Darda started to leave and stand (in prayer), but Salman said to him: 'Sleep.' So he slept. Then he went to stand (in prayer) but he said to him: 'Sleep'. So he slept. When the morning (Fajr) came,Salman said: 'Get up now. 'So he got up to perform Salat. Then he (Salman) said: 'Indeed yourself has a right upon you, your Lord has a right upon you, your guest has a right upon you, and your family has a right upon you. So give each the right they are due. The Prophet ( may the peace and blessings of Allah be upon him ), and that was mentioned to him, so he said: 'Salman has told the truth.'"
[ Jami` at-Tirmidhi ]
The Messenger of Allah ( may the peace and blessings of Allah be upon him ) confirmed the same meaning for `Abdullah bin `Amr ( may Allah be pleased with him ): Narrated `Abdullah bin `Amr ( may Allah be pleased with him ):
Allah's Messenger ( may the peace and blessings of Allah be upon him ) entered upon me and said, "Have I not been informed that you offer prayer all the night and fast the whole day?" I said, "Yes." He said, "Do not do so; Offer prayer at night and also sleep; Fast for a few days and give up fasting for a few days because your body has a right on you, and your eye has a right on you, and your guest has a right on you, and your wife has a right on you.