A person does not need a large source of income to invest. A person can start investing only if they have a reasonable income. Because it is very important to keep your investment consistent because if your investment is not consistent then you can fall far behind the goal of building your portfolio.
You may not require to have a large source of income to start investing but it's necessary and a plus if you can have such a large sources of income as an investor in bitcoin or any asset. It will help you to invest comfortably build a much bigger portfolio without having to withdraw your bitcoin investment prematurely due to extra responsibilities that your small income can't carry. Because it's not sufficient to make room for emergency funds without having to short live your investment due to emergency.
Nobody needs to be very rich or have multiple sources of income to enter Bitcoin investment, what you need is discretionary fund. You can start with what you can and expand as your income starts to increase or if you can cut down on your expenses. In reversal an investor can reduce the amount for accumulation if their basic expenses starts to increase and they don't have a discretionary fund. What is important is so far you're earning money you should try to cut out something to accumulate Bitcoin if you're on DCA method. Let stoping be your last option, even if you were to stop for an unavoidable reasons like lose of job you should have the mindset of continuing when you get back on your feet.