What appears to be the case is that there is nothing wrong with you using these points that are offered by the airline companies and benefitting from them to reduce the price of the airline ticket, because this comes under the heading of selling the tickets for less than the usual price, if he is going to pay some of the price. This is permissible according to the majority of scholars, because sales and rentals are based on mutual consent from both parties. Allah, may He be exalted, says (interpretation of the meaning): O you who believe! Eat not up your property among yourselves unjustly except it be a trade amongst you, by mutual consent [an-Nisa' 4:29]. If the seller agrees to sell his product for less than the usual price, that is permissible.
See the answer to question no. 7842.
Al-Hawaafiz at-Tijaariyyah by Dr. Khaalid al-Muslih, p. 160-167
A similar case is if the customer will get the tickets for free after some time. This is also permissible, because it is a gift from the seller to the purchaser. Ibn Rushd said: There is no problem with being easy-going with regard to the price when selling, or reducing it.
See: Al-Hawaafiz at-Tijaariyyah, p. 164
However it is essential to be careful in that regard and ensure that the price of the original ticket from this company was not greater than the price from similar companies, because the purchaser is only tempted to buy because of what he was hoping for of advantages or discounts after that.
Shaykh Ibn Uthaymeen (may Allah have mercy on him) was asked:
We have a car repair workshop and carwash; we have printed cards on which it is written: Collect four cards for oil change and car wash, and get a car wash for free. Is there anything prohibited in what we are doing? Perhaps you could give us some guidelines with regard to contests and the like?
There is nothing prohibited in that so long as the price has not been increased for the sake of offering this gift.
But if the customer will either be a winner or a loser, then this is not permissible, because if he will be either a winner or a loser, then it comes under the heading of gambling. But if he will either be a winner or will lose nothing, then he will not be harmed at all; either he will gain something or he will not gain anything, but he will not lose anything.
End quote from al-Liqa' ash-Shahri, 1/25
For more information please also see fatwa no. 22085
And Allah knows best.
Reproduced from Islam QA