the ya' because of the vocative particle. The meaning is: I seek refuge in You, O my Lord, and establishing the ya' is permissible.
Surat al-Mu'minun from (verse 99 to verse 104).
الْيَاءُ لِلنِّدَاءِ؛ الْمَعْنَى: أَعُوذُ بِكَ يَا رَبِّ، وَإِثْبَاتُ الْيَاءِ جَائِزٌ.
سُورَة الْمُؤْمِنُونَ من (آيَة ٩٩ آيَة ١٠٤).
