Bismillahi Al-Rahmani Al-Rahim

 Swearing Using the Prophet (Allah bless him and give him peace) Revisited
Q
 Can you please refer me to one of the classical books of the Hanaabilah that make an exception with regards to swearing an oath by our beloved Prophet - SallAllahu 'Alaihi wa-sallam - such that it is binding and requires atonement if broken?

With regards to Ibn Qudaamah considering swearing an oath by other than Allah Makrooh, then being very honest, this is what it seems by reading his words in Muqni'. However, his words in al-Mughni portray the opposite, where he begins his discussion by affirming the Tahreem, and then citing the relevant Nusoos for it. Then he mentions the arguments of the opponents, and begins his refutation by saying.. "wa lanaa…". As one notices, he says at the end of his discussion, that even if we do not consider it as Haraam, then it is Makrooh.

And Allah knows best.

 A
 al-salamu `alaykum wa rahmatullahi wa barakatuhu

Of the sources I mentioned in the original message (Al-Muqni` , Al-`Uddah, Nail Al-Ma'arib , Kash Al-Mudhadarat , and Al-Raudh Al-Murbi`, and Kashf Al-Mukhadarat) only Kashf Al-Mukhadarat mentioned both that is is haram and that it is binding  (see pages 2:460-61). These are all short books, and I am sure that you will find the same things in the late longer books such as Ghayat Al-Muntaha, Kashshaf Al-Qana` , Sharh Al-Muntaha, and Al-Insaf.

It is not odd at all to find Ibn Qudamah says one thing in one of his earlier books, like Al-`Umdah or Al-Muqni`, that is not exactly what he has in Al-Mughni. Sometime he does not mention an issue in an earlier book that is mention in a later, and sometimes he clearly mentions an issue in an earlier book and in a later book seems to support the opposite. If you wish, compare what he says about women covering their hands during prayer in Al-`Umdah and Al-Mugni.

And Allah knows best.
wa al-salamu `alaykum
--musa