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.