"And he turned their rivers into blood. At first, they would fill their cups together, and Israel would find water in their cup while Egypt found blood. They would then fill their cups again, and the Egyptian would say to the Israelite, 'Let us both drink together,' and both would put their mouths to the cup, with the Israelite drinking water and the Egyptian drinking blood. Rabbi Avin said, 'All the water that the Egyptians drank was taken from Israel with blood, and that is how they became wealthy. For if they had taken it without blood, it would have turned to blood.' Rabbi Yosei says, 'This is derived from the verse (Exodus 3:22) "And a woman shall ask of her neighbor," referring to the spoils of Egypt that the Israelites were commanded to request before leaving.'"