Kiddushin (39b): R’ Yaakov said: “There is no reward for mitzvos in this word. For example, the Torah says concerning the two mitzvos of honoring parents and sending the mother bird from her nest, that one’s life will be prolonged and go well. A proof that there is no reward in this world can be seen if someone’s father asked him to climb up the a nest to fulfill the mitzva of sending away the mother bird and thus fulfill both these mitzvos and yet he falls and dies on the way down the ladder. Obviously there would be no happiness or long life resulting from doing these mitzvos in this world, so it must be that the reward of mitzvos is in the next world. However, perhaps this scenario has never happened and thus there is no proof? R’ Yaakov in fact saw this happen… Yet R’ Eleazar has asserted that those who are involved in mitzvos are not harmed? … But the case that R’ Yaakov saw involved a weak ladder so that harm was likely and where harm is likely one must not rely on miracles. This principle of not relying on miracles is learned from Shmuel who was afraid of being killed by Shaul. [Thus, the principle that there is no guarantee of reward in this world has been proved]. If Acher [Elisha ben Abuyah] had understood this principle propounded by his nephew R’ Yaakov he would not have sinned. Acher saw something of this nature. Others say that he saw the tongue [from his mutilated corpse] of the righteous Chutspis being dragged in the street by pigs. He lamented, “The mouth that has uttered pearls of Torah now licks the dust.” Thereafter he rejected Torah observance and became a sinner.