Hiskashrus refers to a person binding himself to the True Tzadik and specifically to Rebbe Nachman of Breslov.

Prayer Sweetness in prayer is experienced according to a person's level of hiskashrus to Tzadikim that are Shomer Habris.[2] Saves Sinners In the letter sent to the men of Tchrin after the passing or Rebbe Noson, It mentions how shortly before his passing, he declared that even the most severe sinner, Heaven forbid, if he clings himself to Rebbe Nachman, he will for sure end up repenting and will receive a rectification.[1]

[1] Eitzos Mevoaros- Hischazkus #30 [2] Hishtapchus Hanefesh 71