What is the basis for establishing legal testimony (Shahadat)?

Primary text

The foundation for legal testimony rests upon the Quran, the Sunnah, consensus (Ijma), and necessity (Ibrah). The evidence from the Quran mandates that testimony requires two men from the believers for financial matters, or one man and two women from those deemed trustworthy among the witnesses if two men are unavailable (Quran 2:282). Further divine command requires witnessing just men in contracts (Quran 32:2) and requires witnessing transactions (Quran 2:282).