Bhisma Ekadasi

Bheeshma Pitamaha or Devavrata is famously known for his oath of life long celibacy. He is one of the strongest characters in mahabharata and also a famous warrior, who could keep Arjuna also at bay on his day. But he is also a very renowned devotee of Lord Krishna. He is the one who proposes Krisna's name for top honor during RajaSuya Yaga performed by Dharmaraj. He also directs Kauravas to listen to Lord Krishna's words and stop war as Lord Krishna knows fully what would happen in the war. Bhisma figures in list of great devotees as given below sloka.

PRAHLADA-NARADA-PARASARA-PUNDARIKA-VYASA-AMBARISA-SUKA-SAUNAKA- BHISMA-DALBHYAN RUKMANGADA UDDHAVA-
VIBHISANA-PHALGUNA ADIN PUNYANI IMAN PARAMA BHAGAVATAN MANAMI (SRI PADYAVALI-52, TADBHAKTANAM MAHATMYAM)
"Prahlada, Narada, Parasara, Pundarika, Vyasa, Ambarisha, Sukhadeva Gosvami, Saunaka Rsi, Bismadeva, Balbhya Rsi, Rukmangada, Uddhava, Vibhisana, Arjuna, etc. to all of these great personalities, I pay my humble obeisances. "

Lord Krishna makes a promise not to touch weapon in the kurukshetrsa war and Bhisma challenges Lord himself stating that he would make Lord touch weapon. Kind hearted Almighty Krishna, wanted to give victory in this small challenge to his devotee Bhisma. One day when Bhisma starts killing Pandava army and Arjuna was not in a position to stop Bhisma. For a moment Krishna jumps out of charriot and takes weapon of sudarsana chakra pretending to kill Bhisma. In this way Lord Krishna displayed to world how much he valued Bhisma and his challenge.

When Bhisma is on his death bed(ampasayya) Krishna takes Dharmaraj to him so that Dharmaraj can learn more details of Dharma from the veteran. In the same context Bhisma gives Vishnu Sahasranama Stotra that is praying lord with 1000 names. Today Vishnu Sahasranama has become one acumen of the devotees who are on philosophical path. (Need to mention here that Late MS Subbalakshmi has given more popularity to it with her voice)

Bhisma who has gotten a boon from his father for his strong character, pitru bhakti and vow he has taken for his father. The boon is called svachanda Marana, means ability to time his death at his wish. During war he generously gives Pandavas secret to stop him in war. He waits on deathbed for auspicious Uttarayana Kalam and attains niryana on Astami of auspicious magha masa. The ekadasi that follows is named after him as Bhisma Ekadasi. It is believed that Fasting on this particular day and spending time in Lord Vishnu's names can free people from the sins.