ANSWER:

If there is space inside the masjid yet they insist on praying outside, they won’t be rewarded. Sheikh Ibn Othaimeen says that the prayer is invalid if there is a place inside the masjid and people pray outside it!

 

Here in my country people tend to sit outside the masjid on a field going late to prayer as they are lazy to use stairs. Is it valid since it is said in a hadith “When Friday arrives, angels are over the door of every mosque to record those who arrive one by one. When the Imam sits to begin, they close their scrolls and come to listen to the reminder”