The Messenger of Allah ﷺ used to like to make supplication three times and seek forgiveness three times.
أن رسول الله ﷺ كان يعجبه أن يدعو ثلاثا، ويستغفر ثلاثا.
Abu Dawud (1524) and Ahmad (3744) narrated it, and Ibn Hibban (923) graded it sahih, all of them through the route of Israil, from Abu Ishaq, from Amr bin Maymun, from Abdullah, who mentioned it. Its isnad is sahih.