"There used to be a very good custom in Jerusalem: a table-cloth was spread at the door – – – so long as it was in place, guests would enter the house. When it was removed, they would not." ~~ Talmud, Bava Batra
"Who lodges a scholar in his home is as one offering first-fruits [Shavuot] in the Temple. " ~~ Leviticus (Vayikra) R.
"Let a stranger live with you, and he’ll estrange your way of life." ~~ Apocrypha: Ben Sira