After saying the opening takbir and before reciting al-Fatihah, it is Sunnah to say a quiet opening supplication. An authentic wording narrated by Abu Hurayrah is: "Allahumma ba'id bayni wa bayna khatayaya kama ba'adta bayna al-mashriqi wa'l-maghrib; Allahumma naqqini min khatayaya kama yunaqqa ath-thawbu al-abyadu min ad-danas; Allahumma-ghsilni min khatayaya bi'l-ma'i wa'th-thalji wa'l-barad" (O Allah, distance me from my sins as You have distanced the east from the west...). Another authentic wording is "Subhanaka Allahumma wa bihamdika, wa tabaraka-smuka, wa ta'ala jadduka, wa la ilaha ghayruk." Any of the confirmed wordings may be used, and it is a Sunnah, not an obligation, so the prayer is valid without it.
Evidence — the daleel
On deen2u
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.