Tradition
St. Ambrose
Letters
Book 63 › Section 105
105. Love hospitality, whereby holy Abraham found favour, and received Christ as his guest, and Sarah already worn with age gained a son; Lot also escaped the fire of the destruction of Sodom. You too can receive Angels if you offer hospitality to strangers. What shall I say of Rahab who by this means found safety?
Source: Letters (New Advent)