How can a Muslim be certain about the supplication of Sayyid al-Istighfar (the Master of Seeking Forgiveness) – "O Allah, You are my Lord; You created me, and I am Your servant..." – so that he may enter Paradise if he dies on that very day or night?

To achieve certainty (yaqeen) in supplication (du’a), a Muslim must utter it believing in its general and specific meanings, sincerely from the heart, and affirming its reward. Whoever says it with these characteristics will be among the people of Paradise.