This is true for spouse and dependent children, that is that proof of income is not required but in case this person is wanting to sponsor parents, grandparents or other relatives, go to http://www.cic.gc.ca/english//information/applications/guides/5196E10.asp and scroll down to table 3. That will tell you how much you need per year for your own family and the people being sponsored.
If sponsoring parents or grandparents or other relatives, you can also ask your spouse to co-sign the application so you can count their income as well.