The last 5 days of the month of Kartika are traditionally known as the Bhisma Panchaka or the Vishnu Panchaka. Grandfather Bhisma fasted for these five days, as arranged by Lord Sri Krishna, preparing to give up his life. In the Hari Bhakti Vilasa it is said that if one is capable, one should observe

The last five days of Kartik beginning with Utthana Ekadasi on November 25 and ending on the Purnima on November 29 are known as Bhisma Panchaka. These are the final days of Grandfather Bhisma’s mortal existence when he instructed King Yudhisthira on various aspects of material and spiritual life in the presence of Lord Krishna