Answer
(Fatwa: 1201/885=H/1429)
If the time is fixed to pay installments, then the easiest way for you is to deal with the company saying (for example): “I purchase the vehicle for four thousand rupees and I will pay the amount in installments in so and so time”. If the company agrees, this purchase on credit will be valid and correct. But, if this very dealing is made in this way that you buy the car in three thousand rupees and pay installments as per four thousand rupees, then the dealing will be unlawful.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband