Not graded
Bulugh al-Maram 504b
وَفِي رِوَايَةٍ لَهُ: فَبَعَثَ مُنَادِيًا يُنَادِي: اَلصَّلَاةُ جَامِعَةٌ 1 .
1 - مسلم برقم (901) (4).
In another narration of Muslim:
"He (ﷺ) sent an announcer to announce: The prayer is (to be offered) in congregation".
Cited in Bulugh al-Maram (No. 504b).