The words Podo Besholom were said by the Alter Rebbe as he was told about his release from Prison in Peterberg. To celebrate the day, which was made the Rosh Hashono of Chassidus, the Chassidim of the Mitteler Rebbe (or some say of the later Rebbeim) composed the Nigun Podo Besholom.
The first part is calm and expresses thanks to Hashem for his kindness. The last part of the Nigun is fast and expresses our great Simcha (joy) in the Alter Rebbe being freed and the ability for Chassidus to flourish and spread resulting ultimately with the Geula Sheleimo - may it be now!
More info on the Nigun here: www.chabad.org/140693