Guidance on Ibn 'Umar's fasting on the day of doubt, despite his narration of the hadith on completing the month

Question:
May Allah reward you. This questioner says: I am confused by the action of Ibn 'Umar (may Allah be pleased with him and his father), for he used to fast on the thirtieth day if clouds or rain prevented the sighting of the new moon. How could he fast when he is the narrator of the hadith in al-Bukhari: "If the sky is overcast for you..."

Answer:
We told you that this was his ijtihad (independent legal reasoning) (may Allah be pleased with him). As for the hadith, it is contrary to this; it prohibits fasting on the day of doubt. Yes.