Asalamualikum,
When praying a 4 rakat Salah, whether it is sunnah or fard, do we recite a surah after reciting Fatiha on the third and fourth rakat ?
Does this apply to all 4 rakat salah?
Recitation of Aayaat after al-Faatihah in the last two Rak'ahs
"He used to make the last two rak'ahs about half as long as the first two, about fifteen aayaat, and sometimes he would recite only al-Faatihah in them."
Sometimes "he would let them hear an aayah or so."
"They would hear the tones of his recitation of "Glorify the name of your Lord Most High" (A'laa 87:19) and "Has the story reached you of the Overwhelming ?" (Ghaashiyah 88:26)."
Sometimes "he would recite "By the Sky and the Night-Visitant" (Taariq, 86:17), "By the Sky, (displaying) the Constellations" (Burooj, 85:22), and similar soorahs." Sometimes "he would recite "By the Night as it conceals" (Layl 92:21) and similar soorahs."
Therefore, the above indicates that it would be Sunnah to recite as well as not.
And Allah knows the best
The Prophet's Prayer -Shaikh Al-Albani