Hadithcore
Riyad as-Salihin, 1096

Abu Hurairah (May Allah be pleased with him)reported:

The Messenger of Allah (ﷺ) said, "Let the Imam stand in the middle (so that those praying behind him should be standing both on his right and his left) and close the gaps." <b>[Abu Dawud]</b>.

وعن أبي هريرة رضي الله عنه قال قال رسول الله صلى الله عليه وسلم‏:‏ ‏

‏وسطوا الإمام، وسدوا الخلل‏

‏ ‏(‏‏(‏رواه أبو داود‏)‏‏)‏‏.‏

References1 variant
In-Book Reference
Book 8, Hadith 106
Sharh · explanationclick to expand
<b>Guidance from the Hadiths:</b><br> 1) Supererogatory prayers are among the best virtues. If a person performs them regularly every day, Allah will build for him a house in Paradise.<br> 2) The Rawātib (regular Sunnah prayers) are 12 Rak‘ahs, to be offered along with the obligatory prayers.<br> 3) Allah Almighty is merciful towards His believing servants who offer the prayer, as He opens to them the gates to goodness so that they can reap abundant rewards.