What is the evidence for the validity of requesting a receipt in financial transactions, given that I based my request on the verse of debt from Surat Al-Baqarah, yet I felt as if I hurt someone who views trust as more important than written documentation?

Documenting contracts and transactions is permissible due to people's need for it. Jurists have differed on the ruling regarding the command to write and attest, with two opinions:

The first is that the command is for recommendation (nadb), which is the view of the majority of jurists, both early and later generations. They base their argument on the Almighty's saying: ﴿فَإِنْ أَمِنَ بَعْضُكُمْ بَعْضًا فَلْيُؤَدِّ الَّذِي اؤْتُمِنَ أَمَانَتَهُ﴾ [If one of you trusts another, let the one who is trusted fulfill his trust]. They argue that the command for attestation and writing is for guidance and preserving rights, not for obligation.

The second is that the command is for obligation (wujub). They base their argument on the apparent command in the verse of debt, and that it is a definitive ruling and not abrogated.

The preponderant view is that of the majority, deeming it recommended. Documenting contracts has general benefits, including: safeguarding wealth, preventing disputes, avoiding invalid contracts, and removing doubt over time.