Ibn Majah

Hadith Commentary:

This means that this prayer is exactly in accordance with the prayer of the Messenger of Allah (sallallahu alayhi wa sallam), and yet you are astonished at it.

"La umm laka" is an expression the Arabs use at times of rebuke and reprimand, similar to "thakilatka ummuk," meaning "may your mother weep over you."

Abdullah ibn Abbas (radi Allahu anhu) was displeased with Ikrimah for not yet knowing the complete method of prayer and for objecting to someone as virtuous as Abu Hurairah (radi Allahu anhu).

Hadith Commentary:
(1)
It has been mentioned earlier that the rulers from Banu Umayyah abandoned the transitional takbirs (takbirat al-intiqal) or would say them very quietly; therefore, the hadith scholars established chapters regarding the transitional takbirs in order to clarify their status, so that this Sunnah would not become completely neglected.
Another purpose is that these takbirs should encompass the entire transition, from its beginning to its end.
It is generally observed that when "Allahu Akbar" is said for prostration (sujud), it is finished even before reaching the prostration.
Imam al-Bukhari rahimahullah has given a warning that when going into prostration, the takbir should be said in its entirety, meaning "Allahu Akbar" should cover the whole transition.
(2)
Ibn Abbas radi Allahu anhu said to Ikrimah, "May your mother not remain," but by this he did not intend its literal meaning, nor was it meant as a supplication against him; rather, it is an idiom which the Arabs use for scolding or rebuke.
Its literal meaning is not intended.
Ibn Abbas radi Allahu anhu rebuked his distinguished student Ikrimah because he was unaware of this Sunnah, even though it pertains to the daily prayer.