Is commissions payable an expense or liability in income statement in accounting? In income statement?

Commissions payable is a liability shown on the balance sheet.

Liabilities are not reported in income statements. If you are paying commissions, the entry to accrue commissions payable is

dr. Commission expense
cr. . . .Commissions payable

The expense is in the income statement, the liability is in the balance sheet. The above applies to commissions you pay to employees or contractors.

If the commission is for stock investment purchases or sales, it is not reported in the income statement at all, nor accrued as a liability. It is used to determine the purchase price or sales proceeds of stock investments.