 The Tanya mentions that one should recite "Tikkun Chatzot" every night if one can.It then suggests that if one cannot do so every night, he should do so on Thursday nights, as a preparation for the Shabbat.Tikkun Chatzot is divided into two parts; "Tikkun Rachel" and "Tikkun Leah", named for the two wives of the Patriarch Jacob.