Abu Saeed Khudri reported,

The Messenger of Allah ﷺ used to seclude himself for worship during the middle ten days of Ramadan. The narrator continued the hadith in similar fashion, except that he said, "Let him remain in his place of seclusion," and he said, "with his forehead covered in mud and water."

Muslim 2770

Sahih

و حدثنا ابن أبي عمر حدثنا عبد العزيز يعني الدراوردي عن يزيد عن محمد بن إبراهيم عن أبي سلمة بن عبد الرحمن

عن أبي سعيد الخدري رضي الله عنه أنه قال

كان رسول الله ﷺ يجاور في رمضان العشر التي في وسط الشهر وساق الحديث بمثله غير أنه قال فليثبت في معتكفه وقال وجبينه ممتلئا طينا وماء

مسلم 2770صحيح
Contents
Reference
Commentary
Ayat
Collection
Sahih Muslim
Book
Fasting
Chapter
Virtue of Laylat al-Qadr, encouragement to seek it, its location, and the most likely times to seek it
Numbering
Darussalam 2770
Muslim 2770