Abu Ahmad reported that Ibn Masud said, "The Prophet ﷺ liked to make supplication three times and to seek forgiveness three times."
حدثنا يحيى بن آدم حدثنا إسرائيل وأبو أحمد حدثنا إسرائيل عن أبي إسحاق عن عمرو بن ميمون
قال أبو أحمد عن ابن مسعود قال كان النبي ﷺ يعجبه أن يدعو ثلاثا ويستغفر ثلاثا
Its isnad is sahih. Abu Dawud narrated it (1:561), and Munziri said (1468), "Nasai also related it." Haythami quoted in Majma al-Zawaid (10:151) a hadith from Ibn Masud, "The supplication most beloved to the Messenger of Allah ﷺ was that he would repeat it three times," and said, "Tabarani related it in Al-Awsat, and its narrators are trustworthy, except that Abu Ubayda did not hear from his father."This is an abridgment of the hadith found here, so including it among the "Zawaid" is a mistake, since Abu Dawud and Nasai had already narrated it.