ZUHR: Here, the Prophet (PBUH) used to recite surah al-Fatihah and two surahs in the first two rak'ahs, making the first longer than the second. (Bukhari & MusIim)
Sometimes, he would lengthen it to the extent that "the zuhr prayer would have started, and someone could go to a plain (al-Baqi), fulfil his needs, come back, make his ablution, and then come (to the mosque) while the Messenger of Allah (PBUH) was still in the first rak 'ah, it is that long." (Muslim) He use to recite in each of these two rak'ahs about thirty verses such as Surah al-Fatihah followed by:
Surah as-Sajdah (Q32) (Muslim);
Surah Taariq (Q86) (Abu Daud);
Surah Buruuj (Q85) (Abu Daud),
Surah Layl (Q92) and similar surah (Trimidhl)
Surah Inshiqaaq (Q84) and similar surah (Ibn Khuzaimah),
You may wonder how the companions knew what the Prophet (PBUH) was reciting silently. The answer is that "they could tell what he was reciting in zuhr and asr from the movement of his beard." (Bukhari) Therefore, endeavour to move your lips even when reciting quietly. In the last two rak 'ah of the zuhr prayer, the Prophet (PBUH) would make them "about naif"as long as the first two, about fifteen aayah (verses) (Muslim),
and sometimes he would recite only at-F'atihah in them." (Bukhari & Muslim)
This does not require sujud sahw (prostration for forgetfulness) as commonly held be cause of the number and strength of the ahadith which attribute such practices to the Prophet (PBUH). He (PBUH) sometimes would "let them (the companions) hear a verse or so." (Thn Khuzaimah)
Also, they used to hear the tones of his recitation of Surah al-A 'laa (Q87) and Surah Ghaashiyah (Q88). (Bukhari & Tirmidhi)
ASR: The Prophet) used to recite surah al-Fatihah and two surahs in the first two rak'ahs making the first longer than the second", (Bukhari & Muslim)
and "they used to think that he did it so that the people could catch the rak 'ah" (Abu Daud)
He used to recite about fifteen verses in each of the first two rak 'ahs,...and he used to make the last two rak 'ah about half as long as the first two." (Abu Daud)
For the first two rak' ah, he (PBUH) used to recite the surah mentioned under zuhr (above) while he "would recite al-Fatihah in the last two." (Bukhari & Muslim)
He would let them hear a verse or so sometimes. (ibid)
(Based on ’The Prophet’s Prayer Described’ by Sheikh Muhammad Al-Albaani)