This regulation (29 CFR 2550.408b-1) describes the terms, under section 408(b)(1), whereby plans loans to participants and beneficiaries are exempt from ERISA's prohibited transaction rules. Among other things, the regulation describes the specific provisions regarding such loans that must be included in the plan document for the statutory exemption to apply.
The latest form for Loans to Plan Participants and Beneficiaries Who Are Parties in Interest with Respect to the Plan Regulation expires 2023-07-31 and can be found here.