What is the authenticity of the Hadith: "O Allah, I ask You for a mercy from You by which You guide my heart, unite my affairs, ward off tribulations from me, mend my religion, safeguard my unseen, elevate my seen, beautify my deeds, whiten my face, inspire me with guidance, and protect me thereby from all evil. O Allah, I ask You for pardon and well-being in this world and the Hereafter," and the reward associated with it: "Whoever says them and teaches them to people, Allah will remove his distress and prolong his joy"?

The long supplication (du'a) of Ibn Abbas mentioned in the question is not authentically reported from the Prophet (peace be upon him), and scholars have deemed it weak. As for the hadith about Ibn Abbas spending the night at his aunt Maymunah's house, it is authentic, narrated in both Sahih al-Bukhari and Sahih Muslim. It includes the Prophet's (peace be upon him) supplication asking for light, but with different and shorter wording. The addition, "Whoever says them and teaches them to people, Allah will remove his distress and prolong his joy," is not found in any of the narrations of the aforementioned weak hadith.