Have you ever heard of such a thing? I have. What, then, is it all about? First, we must ask, where does such a notion come from? Scripture says:

Do not neglect to show hospitality to strangers, for thereby some have entertained angels unawares. Hebrews 13:2 English Standard Version (ESV)

The commentator, Matthew Henry, says the following about these verses:

Be not forgetful to entertain strangers for his sake – We must add charity to brotherly kindness. Here observe:

The duty required—to entertain strangers, both those that are strangers to the commonwealth of Israel, and strangers to our persons, especially those who know themselves to be strangers here and are seeking another country, which is the case of the people of God, and was so at this time: the believing Jews were in a desperate and distressed condition. But he seems to speak of strangers as such; though we know not who they are, nor whence they come, yet, seeing they are without any certain dwelling place, we should allow them room in our hearts and in our houses, as we have opportunity and ability.

Obviously, prudence, wisdom, and discretion should guide our decisions. A single person should be wary of hosting two or more persons of unknown provenance. However, long ago, I guided just such strangers to an inn and bore the cost myself. The reward, if you think it necessary, is twofold, Henry says:

The motive—Thereby some have entertained angels unawares; so Abraham did (Genesis 18,) and Lot (Genesis 19,) and one of those that Abraham entertained was the Son of God; and, though we cannot suppose this will ever be our case, yet what we do to strangers, in obedience to him, he will reckon and reward as done to himself. Matthew 25:35-40, I was a stranger, and you took me in. God has often bestowed honors and favors upon his hospitable servants, beyond all their thoughts, unawares.

So, provide hospitality as you have opportunity and are able. You might even entertain angels unawares.

Hebrews – Dr. R.C. Sproul, YouTube, May 17, 2013