Yud Tes Kislev and Chanukah were two dates on which there was a Magbis. At one point, the Rebbe combine the two into one. On Zos Chanukah 5739, the Rebbe held a farbrengen, and said that one of the reasons for the farbrengen was to talk about the Magbis of Yud Tes Kislev-Chanukah. The Rebbe referred to the Letter of The Alter Rebbe (Iggeres Hakodesh, end of Letter 4) in which he connects tzedaka to the liberation. He also mentioned the that which is quoted by Reb Nechemia of Dubrovna (see Sefer Haminhagim p.71), that it is customary to increase tzedaka giving on Chanukah.