Can You Recite Part of a Surah in Prayer?
Question

After reciting Surat al-Fatihah in each rak`ah, is it permissible to recite only part of one long surah instead of a whole one so that a few long surahs are completed during the whole prayer instead of many short surahs?
Praise be to Allah.It is permissible to recite part of a long surah in prayer instead of reciting a complete short surah, but it is better to recite a complete surah in each rak`ah. This is what the Prophet (peace and blessings of Allah be upon him) usually did. 
Al-Bukhari (762) and Muslim (451) narrated that Abu Qatadah said: “The Prophet (peace and blessings of Allah be upon him) used to recite al-Fatihah and another surah in the first two rak`ahs of Zuhr and ‘Asr.” 
This hadith indicates that “reciting a short surah in full is better than reciting an equal part of a longer surah.” (Sharh Muslim by al-Nawawi (4/174). 
The words of Abu Qatadah - “The Prophet (peace and blessings of Allah be upon him) used to recite…” indicate that the Prophet (peace and blessings of Allah be upon him) persisted in doing that, or that this is what he usually did. (Fath al-Bari, 2/244) 
It was narrated that the Prophet (peace and blessings of Allah be upon him) recited certain surahs in certain prayers. Muslim (727) narrated that Ibn 'Abbas said: “The Messenger of Allah (peace and blessings of Allah be upon him) used to recite ‘Say (O Muslims): “We believe in Allah and that which has been sent down to us…’ [al-Baqarah 2:136 – interpretation of the meaning] and ‘Come to a word that is just between us and you…’ [Al ‘Imran 3:64 – interpretation of the meaning] in the two rak`ahs of Fajr prayer.” This hadith indicates that it is permissible to recite part of a surah in a rak`ah. (Nayl al-Awtar, 2/255) 
Ibn al-Qayyim (may Allah have mercy on him) said:
“The Prophet (peace and blessings of Allah be upon him) taught us to recite a complete surah , and sometimes he would recite a complete surah over the two rak`ahs; or he would recite the first part of a surah. As for reciting the last part of a surah, or the middle part of a surah, it was not narrated that he did that; and as for reciting two surahs in one rak`ah, he would do that in nafil prayers, but it was not narrated that he did that in fard prayers.  The hadith of Ibn Mas’ud (may Allah be pleased with him), “I know the pairs of surahs that the Messenger of Allah (peace and blessings of Allah be upon him) would recite in one rak`ah. He would recite Surat al-Rahman and Surat al-Najm in one rak`ah, or Surat al-Qamar and Surat al-Haqqah in one rak`ah, or Surat al-Tur and Surat al-Dhariyat in one rak`ah, or Surat al-Waqi’ah and Surat al-Qalam in one rak`ah.” This hadith indicates that the Prophet (peace and blessings of Allah be upon him) did that, but it does not specify whether he did it in fard (obligatory) prayers or nafil (supererogatory) prayers. The hadith may mean either. As for reciting one surah in two rak`ahs, he used to do that rarely. Abu Dawud narrated from a man from Juhaynah that he heard the Messenger of Allah (peace and blessings of Allah be upon him) reciting Surat al-Zalzalah in two rak`ahs of Fajr prayer, and he said: “I do not know whether the Messenger of Allah (peace and blessings of Allah be upon him) forgot or did he do that deliberately?” (Zad al-Ma’ad, 1/214-215) 
Shaykh Ibn ‘Uthaymin (may Allah have mercy on him) said: 
“There is nothing wrong with a man reciting one verse from a surah in an obligatory prayer or in a nafl prayer. This may be understood from the ayah (interpretation of the meaning): 
‘So, recite you of the Qur’an as much as may be easy for you’ [al-Muzzammil 73:20]
But the Sunnah – which is preferable – is to recite a surah , and the best is to recite one surah in each rak`ah. If that is too difficult then it is acceptable to divide the surah between the two rak`ahs.” (al-Sharh al-Mumti’, 3/104) 
And Allah knows best.