It is very clear that one doesn't need to have a stable source of income before they can invest in Bitcoin which is very correct because there are times that the kind of source of income we need, we can not get it for some period of time and so instead of waiting for that time it will be advisable to start with the one we have because it is better than not investing at all ( waiting for a stable source of income).
You must have good finance so that you can use part of it for investment and surely have other parts for spendings and emergency fund. If you have good finance but use all of it for investment, it's risky and you will need to cash out your investment just for either spendings or emergency.
So having stable income or not, it's not most important thing for investors and their investment practice. Make sure they have good management on finance and separate their income - that does not need to be stable income - to spending fund, emergency fund and investment capital. If any investor can do it, even lack of stable source of income, he can start and maintain investment very good.