Bulugh al-Maram #488

Narrated Zaid bin Thabit (RA): Allah's (ﷺ) made a small room of a mat (i.e. he used it to designate a space for prayer) and prayed inside it. The people followed him, and they came to pray behind him. The narrator mentioned the rest of the Hadith, and it contains the words: "The most excellent prayer of a person is (that which he prays) in his house except that which is prescribed (the five congregational prayers)." .