Genesis 18:1-5
(1) And the LORD appeared unto him by the terebinths of Mamre, as he sat in the tent door in the heat of the day; (2) and he lifted up his eyes and looked, and, lo, three men stood over against him; and when he saw them, he ran to meet them from the tent door, and bowed down to the earth, (3) and said: ‘My lord, if now I have found favour in thy sight, pass not away, I pray thee, from thy servant. (4) Let now a little water be fetched, and wash your feet, and recline yourselves under the tree. (5) And I will fetch a morsel of bread, and stay ye your heart; after that ye shall pass on; forasmuch as ye are come to your servant.’ And they said: ‘So do, as thou hast said.’
2 Kings 4:9-11
(9) And she said unto her husband: ‘Behold now, I perceive that this is a holy man of God, that passeth by us continually. (10) Let us make, I pray thee, a little chamber on the roof; and let us set for him there a bed, and a table, and a stool, and a candlestick; and it shall be, when he cometh to us, that he shall turn in thither.’ (11) And it fell on a day, that he came thither, and he turned into the upper chamber and lay there.
Talmud Shabbat 127a
R. Judah said in the name of Rav's name: Welcoming guests is greater than welcoming the presence of Shechinah (God)....There are six things, the fruit of which humans eat in this world, while the principal remains for them in the world to come: welcoming guests, visiting the sick, meditation in prayer, early attendance for study, rearing one's children to the study of Torah, and judging one's neighbor in the scale of merit.
Deuteronomy 10:19
Love ye therefore the stranger; for ye were strangers in the land of Egypt.
Pirkei Avot 1:5
Yosei ben Yochanan, man of Jerusalem, says: May your house be open wide, and may the poor be members of your household.
Bavli Talmud Bava Batra 93b
There was another fine custom in Jerusalem. [At the commencement of the meal] a cloth was spread over the door. So long as the cloth was spread, guests entered. When the cloth was removed, no guests entered....
Chaggigah 27a
Rabbi Yochanan and Reish Lakish, who both said: At the time that the Temple stood, it atoned for people. Now, a person's table atones for him or her.
Rav Soloveitchik, Abraham's Journey
The Almighty is the great makhnis orchim. His hospitality made it possible for humanity to exist, for the world to come into being. "To be" means to share in the infinite being of the Almighty. The Almightly, like Abraham, invites people to partake of His boundless existence. Creation is an act of haknasat orchim. Our sages (Berakhot 7b) said that Abraham was the first person to invoke God by the name A-donai. This name is of juridic origin; God owns the world in juridic terms...We are just strangers whom the Almighty has invited into his "tent," which is the universe. How beautiful is the doctrine of tzimtzum, of contraction....What is hakhnasat orchim if not withdrawal by the master from a part of his home so that a stranger can occupy the empty part he vacates?