Can We Recite More Than One Surah in a Rak`ah?
Question

Is it permissible for a worshipper to recite two Surahs in each Rak`ah when praying in congregation or individually? The second Surah which I like to recite in each Rak`ah is Surat Al-Ikhlas.
Praise be to Allah.Can you read more than one surah in a Rak`ah?
There is nothing wrong with a worshipper reciting two or three Surahs after Al-Fatihah , whether he is an Imam or a member of the congregation, except that the Imam should do that only occasionally to show that it is permissible, and without making the prayer too long for the people praying behind him. It is also permissible to do that both in obligatory and Nafl (supererogatory) prayers. 
It is proven that the Prophet (peace and blessings of Allah be upon him) recited two Surahs after Al-Fatihah in many prayers, and these Surahs are known as “pairs”. They are mentioned in several authentic Hadiths. 
‘Amr ibn Murrah (may Allah have mercy on him) said: I heard Abu Wa’il say: A man came to Ibn Mas`ud and said: I recited Al-Mufassal last night in one Rak`ah. He said, “That is too quick, like reciting poetry. I know the ‘pairs’ that the Prophet (peace and blessings of Allah be upon him) used to recite together,” and he mentioned twenty Surahs from Al-Mufassal, two Surahs in each Rak`ah. (Narrated by Al-Bukhaari, 742; Muslim, 822)
Al-Bukhaari (may Allah have mercy on him) included this Hadith in a chapter which he called, “Reciting two Surahs in one Rak`ah.” 
Al-Mufassal is that portion of the Quran which goes from Surah Qaf to An-Nas. 
‘Ilqimah and Al-Aswad (may Allah have mercy on him) said: A man came to Ibn Mas`ud and said: “I recite Al-Mufassal in one Rak`ah.” He said, “That is too quick, like reciting poetry. But the Prophet (peace and blessings of Allah be upon him) used to recite ‘pairs’, two Surahs in one Rak`ah: An-Najm and Ar-Rahman in one Rak`ah, Al-Qamar and Al-Haqqah in one Rak`ah, At-Tur and Adh-Dhariyyat in one Rak`ah, Al-Waqi’ah and Al-Qalam in one Rak`ah, Al-Ma`arij and An-Naz`iat in one Rak`ah, Al-Mutaffifun and `Abasa in one Rak`ah, Al-Muddaththir and Al-Muzzammil in one Rak`ah, Al-Insan and Al-Qiyamah in one Rak`ah, An-Naba’ and Al-Mursalat in one Rak`ah, Ad-Dukhan and At-takwir in one Rak`ah. (Narrated by Abu Dawud, 1396; classed as authentic by Al-Albani in Sahih Abu Dawud) 
When praying Qiyam Al-layl, the Prophet (peace and blessings of Allah be upon him) recited Al-Baqarah, An-Nisa’ and Al `Imran in a single Rak`ah, as was narrated by Hudhayfah (may Allah be pleased with him). (Narrated by Muslim, 772)
Shaykh Ibn ‘Uthaymin (may Allah have mercy on him) said: 
“It is permissible for a person to recite two or three Surahs after Al-Fatihah , or he may limit himself to just one, or he may divide a Surah in two halves (split between two Rak`ahs). All of these are permissible, because of the general meaning of the verse in which Allah says (interpretation of the meaning): 
“So, recite you of the Quran as much as may be easy for you” [Al-Muzzammil 73:20]
And the Prophet (peace and blessings of Allah be upon him) said: “Then recite whatever you can of the Quran.” (Majmu` Fatawa Ash-Shaykh Ibn ‘Uthaymin, 13/question no. 500) 
Shaykh Al-Albani (may Allah have mercy on him) said: 
“The Prophet (peace and blessings of Allah be upon him) would sometimes recite two or more Surahs in one Rak`ah.” (Sifat Salat Al-Nabi (peace and blessings of Allah be upon him), p. 103-105. The Shaykh (may Allah have mercy on him) quotes the Hadiths which have been narrated concerning that, along with their Isnads (chains of narration).)
[This book by Shaykh Al-Albani is available in English under the title The Prophet’s Prayer Described – Translator]. 
Can you recite Surah Al-Ikhlas in every Rak`ah?
With regard to reciting Surah Al-Ikhlas after every recitation in every Rak`ah, it is narrated that one of the Companions did that and the Prophet (peace and blessings of Allah be upon him) approved of it. This is among the evidence concerning the basic question, which is reciting two Surahs in each Rak`ah. 
`Aishah (may Allah be pleased with her) said that the Prophet (peace and blessings of Allah be upon him) sent a man in charge of a raiding party, and he used to lead his companions in prayer, always ending his recitation with Qul Huwa Allahu ahad. When they returned, they mentioned that to the Prophet (peace and blessings of Allah be upon him), and he said, “Ask him why he does that.” They asked him and he said, “Because it is a description of the Most Merciful, and I love to recite it.” The Prophet (peace and blessings of Allah be upon him) said: “Tell him that Allah loves him.” (Narrated by Al-Bukhaari, 6940; Muslim, 813) 
This Hadith indicates that it is permissible to recite Surah Al-Ikhlas in every Rak`ah, although it is not recommended because the Prophet (peace and blessings of Allah be upon him) did not do it or persist in doing it, and the best of guidance is the guidance of Muhammad (peace and blessings of Allah be upon him). 
And Allah knows best.