The past three to six months of pay stubs are the most readily accepted proof of income, but the others should still work, depending on your employment situation.
If you’re a freelancer, independent contractor, or self-employed, the car loan process is a bit more involved, as your income may fluctuate. Prepare yourself for this situation by having proof of up to a year or so of income. You may even want to put together a profit-loss statement to more adequately represent your finances.