Shabbat 21b:10

What is Hanukkah? The Sages taught “On the twenty-fifth of Kislev, the days of Hanukkah are eight. One may not eulogize on them and one may not fast on them.When the Greeks entered the Sanctuary they defiled all the oils that were in the Sanctuary. And when the Hasmonean monarchy overcame and emerged victorious over them, they searched and found only one cruse of oil that was placed with the seal of the High Priest. And there was there to light only one day. A miracle occurred and they lit from it eight days. The next year instituted and made them holidays with  hallel and thanksgiving.

We thank thee also for the miracles, for the redemption, for the mighty deeds and saving acts, wrought by thee, as well as for the wars which thou didst wage for our fathers in days of old, at this season.

In the days of the Hasmonean, Mattathias son of Johanan, the High Priest, and his sons, when the iniquitous power of Greece rose up against thy people Israel to make them forgetful of thy Law, and to force them to transgress the statutes of thy will, then didst thou in thine abundant mercy rise up for them in the time of their trouble; thou didst plead their cause, thou didst judge their suit, thou didst avenge their wrong; thou deliveredst the strong into the hands of the weak, the many into the hands of the few, the impure into the hands of the pure, the wicked into the hands of the righteous, and the arrogant into the hands of them that occupied themselves with thy Law: for thyself thou didst make a great and holy name in thy world, and for thy people Israel thou didst work a great deliverance and redemption as at this day. And thereupon thy children came into the oracle of thy house, cleansed thy temple, purified thy sanctuary, kindled lights in thy holy courts, and appointed these eight days of Chanukah in order to give thanks and praises unto thy great name. For all these things thy name, O our King, shall be continually blessed and exalted for ever and ever.