To invest, you need a source of stable income. If you have a discretionary fund, you will not be able to continue your investment. Because if you do not have a stable income, how will you meet your daily needs and how will you maintain your investment.
You sounds confused here getting started into Bitcoin you doesn't necessarily need a stable source of income before you can started but what you need is your discretionary income, investing in bitcoin doesn't require breaking the bank for you can start accumulating little by little gradually from your discretionary income using the DCA strategy where you can be buying gradually either every weeks or months and hodl, while investing you can also be making plans to increase your financial strength in other to be consistently accumulating Bitcoin, so what you actually need to get started is your discretionary income and not a steady income flow.