Sajdah Sahw is not required if he repeated one Ayah.
فَلَوْ قَرَأَهَا فِي رَكْعَةٍ مِنْ الْأُولَيَيْنِ مَرَّتَيْنِ وَجَبَ سُجُودُ السَّهْوِ لِتَأْخِيرِ الْوَاجِبِ وَهُوَ السُّورَةُ كَمَا فِي الذَّخِيرَةِ وَغَيْرِهَا، وَكَذَا لَوْ قَرَأَ أَكْثَرَهَا ثُمَّ أَعَادَهَا كَمَا فِي الظَّهِيرِيَّةِ، أَمَّا لَوْ قَرَأَهَا قَبْلَ السُّورَةِ مَرَّةً وَبَعْدَهَا مَرَّةً فَلَا يَجِبُ كَمَا فِي الْخَانِيَّةِ وَاخْتَارَهُ فِي الْمُحِيطِ وَالظَّهِيرِيَّةِ وَالْخُلَاصَةِ وَصَحَّحَهُ الزَّاهِدِيُّ لِعَدَمِ لُزُومِ التَّأْخِيرِ لِأَنَّ الرُّكُوعَ لَيْسَ وَاجِبًا بِإِثْرِ السُّورَةِ، فَإِنَّهُ لَوْ جَمَعَ بَيْنَ سُوَرٍ بَعْدَ الْفَاتِحَةِ لَا يَجِبُ عَلَيْهِ شَيْءٌ، كَذَا فِي الْبَحْرِ. (رد المحتار على الدر المختار)
So if he recites it (Surah al-Fatihah a second time) in a Rak’ah from the first two (in Fard prayer) then Sajdah Sahw becomes obligatory (Waajib), due to the delaying of a Waajib, which is the Surah (after Fatihah), as has been mentioned in al-Dhakheerah and others. Likewise if he recites most of it and then repeats it, as has been mentioned in al-Dhakheerah. However, if he recites it once before the Surah and once after it, then it (Sajdah Sahw is not Waajib), as is mentioned in al-Khaniyah, and chosen in al-Muheet, al-Dhaheeriyah and al-Khulasah. Al-Zahidi considered it to be the sound opinion, because it does not necessitate a delay, since Ruku is not Waajib immediately after the Surah, if he recited a number of Surahs after Fatihah then nothing would be required of him (i.e. Sajdah Sahw would not be required), as has been mentioned in al-Bahr. (Imam Ibn Abideen, Radd al-Muhtaar).
As we see in the Nass (text) above, it is only required to make Sajdah Sahw if one repeats the entirety of Surah al-Fatihah or most of it. Repeating a single verse will not necessitate Sajdah Sahw.
There are many other Masail that relate to this one, so if a person has not studied the Fiqh of Salah then this answer or others like it will not be sufficient. Rather they could cause confusion and could be easily misunderstood. Therefore, Muslims are strongly encouraged to study the fundamental Islamic sciences by attending relevant courses and use Q and A as a supplementary means of learning.
And Allah (Most High) Knows Best.
– Answered by Shaykh Noorud-deen (29.06.2021)
Is it sufficient to learn the Deen through Q&A only?
See also (video):