Dr. Monzer Kahf, a prominent economist and counsellor states: “When a partnership is formed by a partnership contract between two or more parties, every decision of its managers would be taken on behalf of all partners on the basis of Wakalah (power of attorney). In other words, contractual partnership implies a Wakalah granted to its management by all partners. Therefore, in contractual partnership, a partner should be keen that the managers do not do any business activity that is prohibited in Shari’ah and any such activity will be the responsibility of each partner. This means that in contractual partnership one must not allow the manager to enter into any Riba-based transaction; it also means that a Muslim may not become a partner in a company that makes such transactions.
Is buying a land by two or more persons [whereby the share in the land of each is known and is recorded (owned) in the name of its owner independently from owners of the rest of the land] a contractual partnership? The answer in usually negative. That is: when two or more persons buy a land together each ownership is independent from the other and one owner has no right to take any decision in regard to the property of any other owner. By the way, this is called in Fiqh “Sharikat al Milk” or partnership in owning in contrast to contractual partnership. I said usually because in some cases one may form a contractual partnership to buy and sell lands for the purpose of making profit.
Consequently, if both partners simply share the buying and ownership on independent basis (although the lot may not be divisible) a Muslim should have nothing to do with what action/activity/contracts the other owner may do or may have done; in other words, buying is permissible. It is also permissible to buy from the other partner after he purchased his own way. However, if the other person is Muslim one should advise them on the prohibition of Riba. Remember, it is the most hated sin that invokes a declaration of war from God and His Messenger (the Qur’an 2: 279).”