What is the ruling on dedicating a two-rak'ah prayer and reciting specific surahs (Al-Layl, Ash-Shams, At-Tin 7 times), then making the supplication of Istikhara or asking for a specific vision, with conditions such as certainty and purity and avoiding speech thereafter, and repeating this for seven days, in order to seek a vision? Is there any Shar'i evidence for this action?

This act is an innovation (bid'ah); because it involves specifying an act of worship in a particular way that was not mentioned in the Sharia. Among these innovations are repeatedly reciting specific surahs in Salatul-Istikhara, or repeating Salatul-Istikhara for seven days. Also among them is the belief held by some that a dream must necessarily occur after Salatul-Istikhara, and scholars have warned against this error. So, when a matter becomes easy for a person after Istikhara, let him know that this is the good. Istikhara is a request for Allah to choose for His servant what is best for him.