Sayyid al-Istighfar…Best Repentance duaa

“Whoever says it during the day with firm faith in it, and dies on the same day before the evening, he will be from the people of Paradise; and if somebody recites it at night with firm faith in it, and dies before the morning, he will be from the people of Paradise”
[Sahih al-Bukhari 8, 75 no318]