Sleeping at Mina during the days of tashriq is obligatory according to the majority of the scholars, and recommendable by others.  It’s enough to stay in Mina till midnight then leave for Mecca, but during the years that the number of pilgrims is crowded, we must take it easy for the people and say sleeping is sunnah, not obligatory. Then people can go for pebbles throwing and then go back to Mecca or Jeddah. The prophet had allowed Abass not to sleep in Mina because he was in charge of offering pilgrims drinks as he allowed camel herders and all those who had work pertaining the pilgrims like securities not to sleep in Mina. Likewise, the person who finds it difficult to sleep in Mina due to lack of space and something alike, it is permissible for them to leave Mina and just for pebbles throwing only.