Elijah the prophet in the Cave of the Patriarchs

Elijah the prophet used to come to study with Rabbi Yehuda Hanasi. Once on Rosh Chodesh, which is longer in prayer, Eliyahu was late and did not come until evening. When he came, our holy rabbi said to him: "Why do you hesitate to come until evening?" He said to him: "Until I raise Abraham up and pour water into his hands for prayer, and also Isaac and also Jacob, the day has passed.

Rabbi Yehuda the Hanasi said to Eliyahu: "Why don't you wake them all at once, and not one by one?

He said to him: "I have no permission to put them all together, lest they exert themselves too much in prayer, and bring the Messiah before his time."

(from the "Baba Metzia")