Next, I discovered two additional versions:

1. The first wording states: “until the sun has risen.”
   Ibn Khuzaymah also recorded it through the route of Ibrāhīm al-Hajrī, from Abū al-Aḥwaṣ, traced back to the Prophet. I remark: besides being mursal, it is weak because of this Ibrāhīm—namely Ibn Muslim. Al-Ḥāfiẓ says in al-Taqrīb: “His ḥadith is soft; he tends to raise mawqūf reports.”

2. The other wording says: “until dawn breaks, or until the reciter leaves the Fajr prayer.”
   Al-Dārimī 346–347, Ibn Khuzaymah, and Aḥmad 2/504 transmit it through Muḥammad ibn ʿAmr, from Abū Salamah, from Abū Hurayrah, as a marfūʿ report.

I comment: even setting aside the narrator’s own uncertainty—which already strips it of value—Muḥammad ibn ʿAmr himself has been criticized for his memory. Moreover, his version is contradicted by al-Zuhrī and Yaḥyā ibn Abī Kathīr, who report from Abū Salamah the clear wording, “until dawn,” with no uncertainty; Muslim and others have transmitted that.

In short, the only wording that stands as authentic in this ḥadith is the last one, and every sound chain supports it. Allah, exalted is He, knows best.