They moved on from Muzdalifah at the end of the night, and stoned the Jamrah and did tawaaf and sa‘i before Fajr
Question

                Is it permissible for a group of physically weak pilgrims to move on from Muzdalifah as soon as the moon disappears, and to be allowed to stone the Jamrah and do tawaaf and sa‘i before Fajr? What is the ruling on that?
Praise be to Allah.
    What they did is permissible and there is 
    nothing wrong with it, because if it is permissible for a person to move on 
    from Muzdalifah, it is permissible for him to do everything that follows 
    that. So if they move on, for example, from Muzdalifah  at the end of the 
    night after the moon disappears, and they reach Mina, then they may stone 
    the Jamrah and go down to Makkah to do tawaaf (circumambulate the Ka‘bah) 
    and sa‘i (go between as-Safah and al-Marwah), and  come back. And if they 
    come back before sunrise, there is no problem with that, because it was only 
    made permissible to move on (earlier) for those who are weak so that they 
    would be able to do the rituals of Hajj before the crowds of people became 
    very great. End quote.