Du’a of Yunus (as)
“No Muslim recites this du’a concerning any matter but Allaah will answer him.” Narrated by al-Tirmidhi and classed as saheeh in Saheeh al-Jaami’, 3383.
So use the du’a of Yunus (as) in your sujood in optional prayers.
The benefits of doing a lot of istighfar:
Ibn Abbas (May Allah be pleased with them) said: The Messenger of Allah (peace be upon him) said,
“If anyone constantly seeks pardon (from Allah), Allah will appoint for him a way out of every distress and a relief from every anxiety, and will provide sustenance for him from where he expects not.” [Abu Dawud].
In another Hadith, Abdullah bin Abbas (May Allah be pleased with them) narrates that Rasulullah (Sallallahu Alayhi Wasallam) said:
“The one who (regularly) says Istighfaar, that is, frequently repent to Allah Ta’aala for sins committed, Allah Azza Wa-Jal will open a path from poverty and difficulties. All sorrow and hardship will be removed, and in its place prosperity and contentment granted. One will receive sustenance from unimagined and unexpected sources.”