Abu Said al-Khudri reported: We used to estimate how long Allahs Messenger ﷺ stood in the noon and afternoon prayers, and we estimated that he stood in the first two rakahs of the noon prayer as long as it takes to recite Alif Lam Mim, Tanzil, i. e. as-Sajda. We estimated that he stood half that time in the last two rakahs; that he stood in the first two of the afternoon as long as he did in the last two at noon; and in the last two of the afternoon prayer about half that time.
Abu Bakr (RA) in his narration has made no mention of Alif Lam Mim, Tanzil, but said: As long as it takes to recite thirty verses.