What is the ruling on the jalsat al-istirahah (short sitting) in prayer according to the four madhhabs, and what are the consequences for one who omits it out of forgetfulness or ignorance?

The hadith indicates the desirability of the jalsa al-istiraha (rest-sitting), which is the sitting after the odd-numbered rak'ahs in prayer. Imam Shafi'i and a group of hadith scholars, as well as one narration from Imam Ahmad, have held it to be desirable. Conversely, the Malikis and Hanafis have deemed it not desirable, and this is the relied-upon position among the Hanbalis. The preponderant view is that it is desirable, because the default understanding of the Prophet's actions (peace be upon him) in prayer is that they are for legislation, and his saying: "Pray as you have seen me praying" supports this. Malik ibn al-Huwayrith, who narrated the hadith, is the same person who narrated "Pray as you have seen me praying." The fact that it was not mentioned in other hadiths does not negate its desirability. Nothing is incumbent upon one who omits it out of forgetfulness or ignorance. If one omits it intentionally, nothing is binding upon him, but it should not be abandoned entirely.