Is it permissible for one partner to pay on behalf of his struggling partner in a joint venture, and for his repayment percentage to increase, if the initial agreement stipulates the determination of each partner's percentage based on the amount paid?

It is permissible to purchase land in installments to build a dwelling upon it and to participate in such a purchase. The land becomes the property of the purchasers immediately upon the contract, and the installments become a debt upon them. If one of the partners defaults on payment, he may sell a portion of his share to the other partners or to an outsider, provided the partners are informed, as they have a pre-emption right (shufa'a). The share can be sold at any price agreed upon by both parties; it is not a condition that it be sold at the original purchase price. Instead of selling, it is permissible to lend to the defaulting partner so that he can fulfill his obligations, and his share remains as it is. The right of pre-emption is mentioned in the Hadith: "The Messenger of Allah, peace and blessings be upon him, ruled with pre-emption in every partnership that has not been divided, whether it be a house or a garden. It is not lawful for him to sell until he informs his partner. If he wishes, he may take it, and if he wishes, he may leave it. If he sells without informing him, then the partner has a greater right to it." Brotherhood and cooperation should be observed, as stated in the Hadith: "May Allah have mercy on a man who is lenient when he sells, when he buys, and when he demands his due."