ALLAAH is Lord of mankind
we shall see this matter in the light of hadith and opinion of ‘Ulama (scholars)
(I) From Hadith :
It was narrated that ‘Ata’ said: Abu Hurayrah said: In every prayer there is recitation. What we heard the Prophet (peace and blessings of Allaah be upon him) say, we tell you, and what he did not tell us about we cannot tell you. WHOEVER RECITES UMM AL-KITAAB (I.E., SOORAT AL-FAATIHAH) HAS DONE ENOUGH, AND WHOEVER DOES MORE THAN THAT, THAT IS BETTER. Narrated by al-Bukhaari, 738; Muslim, 396. (The reference number may vary according to publications)
(II) From the opinion of ‘Ulama (scholars)
The phrase, “Whoever recites Umm al-Kitaab (i.e., Soorat al-Faatihah) has done enough, and whoever does more than that, that is better” indicates that reciting al-Faatihah is obligatory, and that nothing else will do.
It also indicates that reciting a soorah after al-Faatihah is mustahabb(encouraged)
Sharh Muslim 4/105
(b)Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said:
According to the majority of scholars, reciting another soorah (after al-Faatihah) is Sunnah and is not obligatory, because it is obligatory to recite only al-Faatihah.
Al-Sharh al-Mumti’ 3/103
ALLAAH knows best