《太平广记·卷四·神仙四》
后来他俩学成离开，先生脱下一只鞋变成了一只狗，这狗带着苏、张二人向北走，当天就到了秦国。
苏、张学成别去，先生与一只履，化为犬，北引二子即日到秦矣。
Later, after they finished learning and left, the teacher took off one of his shoes and turned it into a dog, and the dog led Su and Zhang north, and they reached the State of Qin that same day.