He left ‘Arafaat before Maghrib because he was sick
Question

                What is the ruling on one who leaves ‘Arafah before sunset because of sickness, weakness or old age?.
Praise be to Allah.
    The most correct opinion is that staying in ‘Arafah until the 
    sun sets is obligatory, because the Prophet (blessings and peace of Allah be 
    upon him) did not leave before the sun set, and if it were permissible he 
    would have left before the sun set, because then it is still daytime and is 
    easier for people. Moreover, if a person leaves before the sun sets, he has 
    forsaken the Sunnah of the Prophet (blessings and peace of Allah be upon 
    him) for the way of the Jaahiliyyah, because the people of Jaahiliyyah are 
    the ones who leave ‘Arafah before the sun sets. If the one who does that 
    does it deliberately, his action results in two things:

    (i)Sin

    (ii)According to the majority of 
    scholars, he has to offer a sacrifice as ransom (fidyah), to be slaughtered 
    in Makkah and distributed to the poor. 

    But if he left ‘Arafah before sunset out of ignorance, he has not sinned but according to the majority of scholars he has to offer a sacrifice, which means slaughtering a sheep in Makkah and distributing it (its meat) to the poor. End quote.