Tosefta zu Dewarim 4:32

Everyone who speculates upon four things, it would have been better that he had not come into this world: What is above, what is below, what came before, and what comes after (Chag. 2:1). One might think [that one may speculate about what occurred] before the Act of Creation, [and thus] the verse states, "[Inquire of the first days,] from the day that God created man on Earth" (Deut. 4:32). [One might think that one may speculate about events] before the order of the seasons (סדרי תקופות) was established (i.e., before the creation of the sun and moon, see Lieberman), [and thus] the verse states (ibid.), "[inquire] from one end of the heavens until [the other] end of the heavens" [but not about what occurred before the creation of heavens]. What is meant by the verse, "from the day that God created man on Earth"? From the day that God created man on the Earth, you may inquire. But you may not inquire about what is above, what is below, what was and what will be.