Is it obligatory for one who could not find a place to spend the night in Muzdalifah except on the road—thus being unable to spend the night there—to return to Mina?

If a pilgrim does not find space in Muzdalifah, or if soldiers prevent him from dismounting there, then there is no blame upon him, as Allah the Almighty says: "So fear Allah as much as you are able." However, if that was due to his negligence, then he must offer a sacrifice (dam) along with repentance.