"Please provide your last three salary slips" is a request built around traditional employment, and it puts freelancers in an awkward spot — not because their income is any less real, just because it doesn't come with the same paperwork by default.
Bank statements showing regular deposits
Several months of statements showing consistent incoming payments demonstrate an income pattern much the way salary slips do for an employee — often the single most persuasive document a freelancer can provide.
Invoices issued to clients
A stack of invoices over time shows both the work being done and what it's being billed at, giving a reviewer a sense of both your rate and your client relationships.
Tax filings or self-employment income declarations
In many countries, an annual tax return or self-employment income statement is the closest equivalent to a salary slip a freelancer can offer, and it's often taken seriously precisely because it's an official filing.
A signed accountant's letter
For larger applications (a mortgage, for instance), a letter from an accountant summarizing income over a period carries real weight, since it's a third party vouching for the figures rather than the freelancer's own documents alone.
A simple self-generated income summary
For smaller, less formal requests, a clean one-page summary of monthly income over the past several months — even self-prepared — is often enough, especially paired with supporting invoices or bank records.