Origin of Bhisma Pancaka
Bhisma Pancaka vrata is named after Bhisma because he got it from the Lord and followed it. This is stated in Rupa Goswami's Mathura-mahatmya (189), where he cites a verse from Padma Purana (which is not traceable today): atha bhīṣma-pañcake, pādme bhīṣmaṁ prati śrī-kṛṣṇa-vacanam— tvayā kṛte vrate paścāt khyāsyate bhīṣma-pañcakam | ye tatra janma-bhūmau me kariṣyanti mahā-vratam | mathurāyāṁ tu gāṅgeyā teṣāṁ bhaktiḥ kare sthitā || Residing in Mathurā During Bhiṣma-pañcaka. In the Padma Purāna, Śri Kṛṣna says to Bhiṣma: O Gaṅgeya, this vow you have followed will henceforth be known as Bhiṣma-pañcaka. They who follow this great vow in My birthplace, Mathurā, find pure devotional service resting in their hand. Bhisma-pancaka is elaborately described in the Uttara khanda of the Padma Purana (ch.124). It is stated there that it is named after Bhisma because he received it from the Lord: bhīṣmeṇaitad yataḥ prāptaṁ vrataṁ pañca-dinātmakam sakāśād vāsudevasya tenoktaṁ bhīṣma-pañcakam ...