The book Musnad al-Firdaws (مسند الفردوس) by [Abū Manṣūr] al-Daylamī (Jr) is a lost work: it is available only partially (in manuscript form), and has, hence, never been published, to my knowledge.
However, Ibn Ḥajar al-ʿAsqalānī has authored a book titled Zahr al-Firdaws (زهر الفردوس), also known as al-Gharā’ib al-Multaqaṭah min Musnad al-Firdaws (الغرائب الملتقطة من مسند الفردوس), in which he has narrated (some) ḥadīths from Musnad al-Firdaws of [Abū Manṣūr] al-Daylamī (Jr).
You may download Zahr al-Firdaws from here:
(1)الغرائب الملتقطة من مسند الفردوس مما ليس في الكتب المشهورة - مخطوط: manuscript transcript in BOK format: https://shamela.ws/rep.php/book/522 [BOK].
(2)الغرائب الملتقطة من مسند الفردوس = زهر الفردوس: published for the first time by Jamʿiyyah Dār al-Birr (جمعية دار البر), Dubai, in 1439/2018: https://www.almeshkat.net/book/14654 [PDF; BOK].
To open BOK (.bok) file, download, extract, and run/install the following “empty/emptied (مفرغ)” version of the Shamela Islamic Library (المكتبة الشاملة) v3.64: https://www.almeshkat.net/book/2288.
There is a published book called al-Firdaws (الفردوس)—also known as Firdaws al-Akhbār (فردوس الأخبار)—which people mistakenly confuse to be the Musnad al-Firdaws (مسند الفردوس) of Abū Manṣūr al-Daylamī.
The truth, however, is that the book Firdaws al-Akhbār is not the same book as Musnad al-Firdaws.
The book Firdaws al-Akhbār is authored by Abū Shujāʿ al-Daylamī—the father of Abū Manṣūr al-Daylamī.
Also, the book Firdaws al-Akhbār contains ḥadīths without the chain of narrators (isnāds).
It is for this reason that the son of the author of Firdaws al-Akhbār, Abū Manṣūr al-Daylamī, had written the book Musnad al-Firdaws, in which he had provided the chains of narrators (isnāds) for the ḥadīths mentioned in the book of his father, and this is why he had named it Musnad al-Firdaws—musnad meaning “provided with isnād(s)”.
You may download the book Firdaws al-Akhbār from here:
