What is the ruling of Islamic law on buying a house at a low price from a person, on condition that the owner resides in it and the buyer pays a monthly rent for the seller's lifetime, and the buyer does not benefit from the house until after the seller's death?

For a sale to be valid, the price must be known. Here, the price is unknown because it includes three things: an upfront payment of 19,000, monthly installments of 400 until death, and the benefit of housing until death. This leads to gharar (excessive uncertainty) and jahalah (ignorance), both of which are forbidden in Sharia. Determining and knowing the price is a condition for the validity of a sale.