Is it permissible to sell by installment, with agreement on the price of the commodity and the value of the installment, without mentioning the number of installments, and without specifying a fixed value or definite dates for the installments for freelancers, and with acceptance of default in the value or timing of payment?

Installment sales are permissible on condition that a known term for the payment of the price is specified. The first forms mentioned are permissible because the term therein is known. As for the second form, where the buyer pays the price as it becomes easy for him, it is not permissible due to the lack of a specified term. If known payment dates are set and the buyer delays in paying an installment or part of it, there is no harm in that.