Related על ברכות 1:3

It happened with Rebbi Yishmael and Rebbi Elazar Ben Azaryah that they were resting in the same place and Rebbi Yishmael was laying down and Rebbi Elazar Ben Azaryah was [standing up] straight. It came time to say Shema. Rebbi Yishmael stood up straight and Rebbi Elazar laid down. Said to him Rebbi Yishmael: “What is this Elazar?” He said [back] to him: “Yishmael, my brother! They say to a person, ‘Why is your beard all grown [so nice]?’ He said [back to them], ‘[it should be sent] against the destroyers’ (i.e. cut off by the scissors). [So too with us] I (Rebbi Elazar Ben Azaryah) who was straight, laid down, you that was laying down, stood up straight?” [So Rebbi Yishmael] said to him: “You laid down to fulfill the words of Bet Shamai, I stood up straight to fulfill the words of Bet Hillel. A different explanation, that the students should not see [that you did like Bet Shamai] and make your words [a] permanent [law].