What is the evidence that the Hadd punishment for rape is that of Hirabah (unlawful warfare/banditry), and not the Hadd of Zina (fornication/adultery), especially if the rapist did not use any weapon, and was it the practice of the Companions to require four witnesses for this crime?

If the rapist did not carry a weapon, he is to be given the hadd punishment for zina (unlawful sexual intercourse). Zina is proven by the testimony of four men, or by confession, or by the appearance of pregnancy coupled with the absence of doubt and the claim of compulsion. The evidence for requiring four witnesses is Allah's saying: (And those who commit unlawful sexual intercourse of your women - bring against them four [witnesses] from among you.) [An-Nisa/15], and (And those who accuse chaste women and then do not produce four witnesses - lash them eighty lashes) [An-Nur/4], and (Why did they not produce for it four witnesses?) [An-Nur/13]. The proof of zina by testimony is very rare. The rapist may be given a discretionary punishment (ta'zir) if he does not confess or if no evidence is established against him, due to the wisdom of concealing sins and not spreading indecency.