Ruling on selling an item on credit for a higher price than if it is paid for immediately
Question

                If one sells an item at Rs.10 against cash payment, can he demand a higher price from a a buyer who wants to buy on 30 days credit. IN other words: 

If an item is sold for Rs. 10 against cash payment, can the seller demand Rs, 11 for the same item from a buyer who wants to buy against 30 days credit. This question needs clarification in the light of Riba .
Praise be to Allah.It is permissible to sell an item on credit for a 
          higher price than if it is paid for immediately, whether the payment 
          is to be made in installments or in one payment at the later date. But 
          this is conditional upon the two parties not separating until they have 
          agreed how the transaction is to be done, whether it is to be paid immediately 
          or deferred. In this case the additional amount is not riba, and there 
          is nothing in sharee’ah to specify the amount of the extra payment in 
          the case of deferred payment. But the Messenger of Allaah 
          
          (peace and blessings of Allaah be upon him) encouraged tolerance in 
          matters of selling, buying, paying off debts and asking others to pay 
          debts.
Fataawa al-Lajnah al-Daa’imah
See Fataawa Islaamiyyah, 
          part 2, p. 335  
        But if 
          he sells it for ten, for example, then the purchaser subsequently wants 
          to delay payment, it is not permissible for the vendor to add anything 
          to that. If he adds something in return for extending the time period, 
          this is riba and is haraam and a major sin. We ask Allaah to 
          keep us safe and sound.
See 
          also the answer to question no. 1231.