How does a Muslim reach the degree of certainty, trust, and reliance upon Allah, and what deeds assist him in that?

We have no knowledge of the authenticity of the story mentioned, but Allah Almighty answers the prayer of the distressed and sincere person, even if they are a disbeliever. This is because distress and sincerity are among the greatest reasons for a prayer to be answered. To attain certainty, it is recommended to continuously ponder the attributes and power of Allah, associate with people of certainty, strive against the self, and maintain sincerity and full devotion when supplicating.