Which is better: borrowing from one's mother to complete the price of purchasing an investment building, or having her participate with capital and a percentage of the rental profits?

Lending money to one's child as a preferential gift is not permissible. A partnership contract should be concluded between you if the son needs a partner. It is not permissible for a partner to guarantee the capital of his partner, as a partner is an agent and a trustee who does not guarantee except in cases of transgression or negligence. It is not permissible to return the mother's capital as a guarantee. However, she can sell her share of the project after its completion at a price agreed upon by both parties.