1. The first explanation is that the order to “pray Fajr in isfār” (full dawn-light) simply means: make sure dawn has actually broken so that you do not rush and end up offering the prayer in the tail-end of the night. In that case, the superlative “greater” in the wording “is greater in reward” is being used outside its normal comparative sense, a usage well attested in Arabic.
2. The second explanation is that isfār refers to lengthening the Qur’an recitation inside the prayer—something recommended—so that they would not finish until the sky had begun to brighten.

Points derived from the hadith

1. It is recommended to perform the dawn prayer at the very beginning of its time.
2. Women may come to the mosque and pray with the men provided there is no fear of temptation and they take care not to display their adornment.

Hadith 3
Jabir ibn ‘Abd Allah (may Allah be pleased with him) reported: “The Prophet ﷺ used to pray Zhuhr during the hājirah (the intense midday heat); ‘Asr while the sun was still bright and clear; Maghrib as soon as it had set; and ‘Isha’—sometimes early, sometimes late. When he saw the people gathered he would pray it promptly, and when he saw them delaying he would postpone it. As for Fajr, the Prophet ﷺ would pray it in the darkness of early dawn.”

Unfamiliar vocabulary

1. al-hājirah: the extreme heat that follows the sun’s zenith, so called because people ‘abandon’ (hajara) their work in that heat.
2. naqiyyah: untarnished, pure—i.e., the sun’s disc was still white, untouched by the yellowing of sunset.
3. “when it had set”: i.e., when the sun had completely disappeared below the horizon.
4. al-ghalas: the mingling of the last darkness of night with the first light of dawn (see above).

Overall meaning
This hadith sets out the optimal times for the five daily prayers. Zhuhr is prayed once the sun has begun to decline from the zenith. ‘Asr is performed while the sun is still white and clear, before any yellowing appears—that is, when the length of an object’s shadow equals its height in addition to the zenith shadow.