كتاب الفضائل
8  
The Book of Virtues
(192)
Chapter: Urging to Observe 'Isha' and Fajr Prayers in Congregation
(192)
- باب الحث على حضور الجماعة في الصبح والعشاء
Riyad as-Salihin 1072
Abu Hurairah (May Allah be pleased with him)reported:
The Messenger of Allah (ﷺ) said, "If they knew the merits of Salat after nightfall ('Isha') and the morning (Fajr) Salat, they would come to them even if they had to crawl to do so."

[Al-Bukhari and Muslim]

This is part of a long Hadith which has already been mentioned. See Hadith No. 1033.
وعن أبي هريرة رضي الله عنه أن رسول الله صلى الله عليه وسلم قال‏:‏ ‏ "‏ولو يعلمون ما في العتمة والصبح لأتوهما ولو حبوًا‏"‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏‏.‏ وقد سبق بطوله‏.‏
Reference : Riyad as-Salihin 1072
In-book reference : Book 8, Hadith 82