"[Avraham] looked up and saw: And behold! three men were standing near him" [Vayeira 18:2]
Rashi explains that the three "men" were actually angels that had been sent to carry out specific missions. One angel was to inform Sarah that she was going to bear a son, another angel was sent to destroy Sodom, and yet another one was sent to heal Avraham. Each angel was to perform only one task, as an angel is never sent to carry out more than one mission at a time.
Rashi goes on to inform us that the angel that healed Avraham subsequently travelled to Sodom in order to save Lot.
Soon after being appointed as rabbi of Brod, R'Shlomo Kluger was given the honor of being the sandak at the bris milah of one of the distinguished members of the town.
However, when he arrived at the shul where the bris was to be held, he noticed that everyone there seemed downcast and dispirited. R' Kluger approached one of his congregants and asked him what was the matter.
"The father of the infant is deathly ill." responded the man. "Being that his end is near, the family decided to delay the bris so that they could name the child after his father."
"Hurry" exclaimed R' Kluger, "bring the father here and perform the bris immediately!"
The father was brought to the shul and the bris was performed. Amazingly, as soon as the bris concluded, the father's medical condition improved! The father's life was, miraculously, no longer in danger. News of the miracle brought about by the new rabbi spread quickly throughout the town.
R' Kluger, however, dismissed the rumors about his "miraculous powers". "It wasn't a miracle at all." he insisted. "I learned to do so from the words of Rashi in Parshas Vayeira. Rashi there explains that the angel that cured Avraham later went on to Sodom to save Lot. But this is perplexing..." continued R' Kluger. "Were there not enough angels available that one had to be sent to carry out two missions?"
"Rather", he answered, "Lot's zchus [merit] was not great enough to earn him an angel that could be sent specifically to save him, so the angel that was sent to cure Avraham was then sent to save Lot.
"It occurred to me," concluded R' Kluger, "that in all likelihood the father's life was being weighed at that very moment. But I was concerned that perhaps the father would not have sufficient merit to deserve a special angel to cure him. But since Eliyahu HaNavi, the angel of the bris, is present when the infant is circumcised, it was possible that he would bring about a recovery for the father as well."
Source: Rabbi Yisrael Bronstein