It is narrated from Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) that he said: "the Messenger of Allah (peace and blessings be upon him) used to offer the Fajr prayer when it was well lit (that is, when the light of morning had spread)."
Imam al-Harith recorded this hadith in his Musnad; however, its chain includes a narrator named Abd al-Aziz bin Aban, whom the imams of narrator criticism have declared a liar and matruk (abandoned). Therefore, technically, this report is very weak and cannot be used as evidence.
Hadith Referenceالمطالب العالية بزوائد المسانيد الثمانية / كتاب الصلاة / 268
Hadith Gradingمحدثین:إسناده موضوع
Hadith Takhrij«حکم الحدیث المطالب العالیہ محققاً تنسیق د. سعد بن ناصر بن عبد العزيز الشَّثري- مکتبہ شاملہ :موضوع. » «انفرد به المصنف من هذا الطريق»