Philo Judaeus De Vita Contemplativa 30

[30] Therefore, during six days, each of these individuals, retiring into solitude by himself, philosophises by himself in one of the places called monasteries, never going outside the threshold of the outer court, and indeed never even looking out. But on the seventh day they all come together as if to meet in a sacred assembly, and they sit down in order according to their ages with all becoming gravity, keeping their hands inside their garments, having their right hand between their chest and their dress, and the left hand down by their side, close to their flank;