There is no income required. However, it is taken into consideration. Usually it is not an issue: the visa officer will assume that you and the spouse applying to immigrate will be able to support yourselves. That is, the immigrating spouse is expected to get a job.
It becomes an issue when the visa officer looks at the file and decides that no, this couple will not be able to support themselves. Then the PR visa can be rejected because of a lack of sufficient income, even though technically no income is required.
For example, in one case, the sponsor was a recent PR himself and had a minimum-wage job. His wife could not speak English or French, and her job in China was not one that she would be able to do here. No transferable skills, no money saved up, etc. The PR visa was rejected based on the visa officer's opinion that the couple would not be able to support themselves.
So when you submit your application, it is a good idea to show your plans for the future: what do the two of you plan to do to support yourselves. If the sponsor is a student but will be graduating soon, he/she can mention what type of job he expects. If the applicant has transferable job skills and relevant education, these should be mentioned. Any money saved or any offers of support from family should also be shown. If the sponsor has a well-paying job already, then less of this is necessary, of course.
To sum up, a sponsor with no job and no income can be found eligible to sponsor, but in this case the application should show how the couple plans to support themselves, with any evidence of this shown.
