According to this website, there is a claim that "It is part of our glorious tradition going back thousands of years to seek a blessing from a Tzaddik for a sick relative (see Talmud Bava Basra 116a)". However, the language they are using is as follows in the Talmud Bava Basra 116a:
The Gemara presents the third homiletic interpretation: Rabbi Pineḥas bar Ḥama interpreted a verse homiletically: Anyone who has a sick person in his home should go to a sage, and the sage will ask for mercy on the sick person’s behalf, as it is stated: “The wrath of a king is as messengers of death; but a wise man will pacify it” (Proverbs 16:14)
Essentially, they are using the word sage. However, as far as I'm aware, a sage and a tzaddik are not necessarily identical in meaning. By "tzaddik" I mean a deeply righteous and "saintly" person whose mere presence causes others to become more spiritually developed and enlightened and causes them to attach themselves to the person. Therefore, this made me wonder a) what is the earliest use of the term tzaddik, both in meaning and in literal form/word b) How long back does the concept of a tzaddik go, even if it wasn't termed a tzaddik necessarily?