Why must one wait twenty minutes after the Adhan before the Fajr prayer?

It is recommended to hasten to pray Fajr, Asr, and Maghrib at the beginning of their prescribed times, due to the hadith of Umm Farwah, may Allah be pleased with her, that the Prophet, peace and blessings be upon him, was asked: "Which deeds are best?" He said: "Prayer at the beginning of its time," narrated by Tirmidhi and Abu Dawud. However, waiting twenty minutes after the dawn breaks for the worshippers to perform ablution, pray the optional Fajr prayer, and complete their preparations is not considered a delay.