When the verse "until the white thread becomes distinct to you from the black thread of the dawn" [Baqarah 2:187] was revealed, the Prophet ﷺ said to me, "That refers only to the whiteness of day distinguished from the blackness of night."
حدثنا أحمد بن منيع حدثنا هشيم أخبرنا حصين عن الشعبي أخبرنا
لما نزلت {حتى يتبين لكم الخيط الأبيض من الخيط الأسود من الفجر} قال لي النبي ﷺ إنما ذاك بياض النهار من سواد الليل
Its isnad is sahih. Abu Dawud narrated it in the Book of Jihad, in the chapter on the words of Allah, Exalted is He, "and do not throw yourselves into destruction" [Baqarah 2:195], hadith 2512, from the hadith of Haywa bin Shurayh with this wording. Ibn Hibban graded it sahih, hadith 1667, as did Hakim according to the criterion of the two Shaykhs, 2/275, and Dhahabi agreed with him. This hadith has many routes of transmission in Tarikh Dimashq by Ibn Asakir and others.His statement "and in charge of the group is Fadala bin Ubayd" appears this way in the narration of Tirmidhi, but the correct version is "and in charge of the group is Abdul-Rahman bin Khalid bin Walid." Alternatively, this may be a different expedition, distinct from the expedition of Abdul-Rahman. And Allah knows best.