Many Disability Pensions (including CPP Disability) are indeed taxable income. If you have received a T-Slip (T4A, T4A(P)) for your pension it must be entered on your tax return and you will be paying tax on it.
Only if you are receiving a "Wage Loss Replacement" or "Long Term Disability" from a plan which you paid for the premiums 100% is the pension "Not Taxable". In cases like these, you will receive no tax slips, and nothing is entered on your tax return.