Is it among the manners of supplication to repeat it three times, and is exceeding that considered an innovation (bid'ah) and forbidden?

The etiquette and conditions of supplication (du'a) have been previously explained. Among its etiquette is repeating it three times at one time, and the intention is not to limit oneself to that and then abandon it. Rather, what the Sharia encourages is persistence in supplication and not discontinuing it.