I heard a man asking forgiveness for his parents while they were polytheists, so I said to him, "Do you ask forgiveness for them when they are polytheists?"He replied, "Did Ibrahim not ask forgiveness for his father?"So I went to the Prophet ﷺ and mentioned this to him, and then this verse was revealed, "And the request of forgiveness by Ibrahim for his father was only because of a promise he had made to him" [Tawbah 9:114].
أخبرنا إسحق بن منصور قال حدثنا عبد الرحمن عن سفيان عن أبي إسحق عن أبي الخليل
سمعت رجلا يستغفر لأبويه وهما مشركان فقلت أتستغفر لهما وهما مشركان فقال أو لم يستغفر إبراهيم لأبيه فأتيت النبي ﷺ فذكرت ذلك له فنزلت {وما كان استغفار إبراهيم لأبيه إلا عن موعدة وعدها إياه}
Grading, its chain of transmission is daif. Tirmidhi transmitted it in the book of tafsir of the Quran, chapter "And from Surah Tawbah," hadith 3101, from the hadith of Sufyan Thawri, with this chain, and he said, "hasan." It is also found in al-Kubra, hadith 2163. Thawri explicitly stated that he heard it directly, as found in the narration of Abu Yaala, 1/280, hadith 335. Hakim graded it sahih, 22/335, and Dhahabi agreed with him. Abul-Khalil is Abdullah bin Khalil Kufi, and Abdul-Rahman is Ibn Mahdi. Abu Ishaq narrated using "an" without specifying direct hearing. Some parts of the hadith have corroborating reports in Hakim, 1/335, and elsewhere. Hakim graded it sahih, and Dhahabi agreed with him.