When is influencing a company's share price—whether by raising or lowering it—considered a reason for prohibiting the sale or purchase of shares? And what is the criterion for determining such influence? Is it permissible to buy and sell a quantity that does not affect the share price?

It is not permissible to manipulate stock prices on the exchange by offering large quantities for sale to lower the price and then buying cheaply. However, if the investor does not intend manipulation, then there is no harm in selling or buying any number of shares at any price, as long as their investment is in shares of companies that are Islamically permissible.