Are there any authentic Hadiths that specify that the remembrance "O Living, O Sustainer, by Your mercy I seek aid; rectify all my affairs and do not entrust me to my soul for the blink of an eye, there is no god but You" should be recited three times after Fajr and Maghrib prayers?

No authentic hadiths have specified the recitation of "O Ever-Living, O Self-Sustaining, by Your mercy I seek assistance; rectify all my affairs and do not entrust me to myself for the blink of an eye. There is no god but You" three times after Fajr and Maghrib. However, it was narrated by Anas ibn Malik that the Messenger of Allah, peace and blessings be upon him, advised Fatimah, may Allah be pleased with her, to say: "O Ever-Living, O Self-Sustaining, by Your mercy I seek assistance; rectify all my affairs and do not entrust me to myself for the blink of an eye" when she wakes up in the morning and when she enters the evening. This hadith is authentic.