Details of the whip itself are derived or inferred from verses in the Torah -- specifically to focus on the process of flogging the sinner. Also, the last mishnah of Makkot: with the list of one who gets lashes to the exclusion of karet, thanks to the inherent humiliation in the lashes. Also, 3 practices were decided by the earthly courts and then approved by the heavenly court - so the Gemara proves that heavenly support through supporting verses. Likewise, a heavenly voice that confirmed 3 other courts' decisions - including backing King Solomon's famous "cut the babt in half" decision, to make it clear that there was no chance that the other woman was the real mother. Plus, the tradition of the 613 mitzvot, with 365 negative ones and 248 positive ones, and how we get to 613 (hint: "Torah tzivah lanu Moshe....").