Sheikh ibn Uthaymeen was asked:
Question: Is it a must to observe the prostration of recitation (Sujood at-Tilawah) whenever one comes across verses marked with this prostration?
First: in regards to the phrase “is it a must”, it’s actually not an obligation to observe this porstration; it’s rather a sunnah no matter how many times one comes across verses marked with this prostration. This statement is supported by Umar’s observance of this particular prostration at one incident during a Jumaa prayer, at which he came across a verse in Surat al-Nahl marked with Sujood and prostrated. In a similar incident, he came across the same verse but he didn’t observe this prostration; he commented, “Allah left us the choice in observing this prostration and didn’t obligate it.”
As for the repetition of this prostration, observing it once is sufficient for who recites the Qur’an regularly and he is not required to repeat it every time.
Source : The series of al-Bab al-Maftooh: number: 62.
Translation by: Abdullah Ibrahim Omran al-Misri.