After his father lost his eyesight, Kaab bin Malik used to serve as his guide. Whenever Ubayy heard the call to prayer on Friday, he would invoke Allah's mercy upon Saad bin Zurara.I asked him, "Why is it that whenever you hear the call to prayer, you pray for mercy upon Saad bin Zurara?"He replied, "Because he was the first to gather us for the Friday prayer in Hazm an-Nabit, in the harrah of Banu Bayadah, at a place called Naqi al-Khadamat."I asked, "How many of you were there that day?"He answered, "Forty."
حدثنا قتيبة بن سعيد حدثنا ابن إدريس عن محمد بن إسحق عن محمد بن أبي أمامة بن سهل عن أبيه
وكان قائد أبيه بعد ما ذهب بصره عن أبيه كعب بن مالك أنه كان إذا سمع النداء يوم الجمعة ترحم لأسعد بن زرارة فقلت له إذا سمعت النداء ترحمت لأسعد بن زرارة قال لأنه أول من جمع بنا في هزم النبيت من حرة بني بياضة في نقيع يقال له نقيع الخضمات قلت كم أنتم يومئذ قال أربعون
Its isnad is hasan. Ibn Majah narrated it in Iqamat as-Salawat, chapter on the obligation of Jumuah, no. 1082, from the hadith of Muhammad bin Ishaq, with the same wording, and he explicitly stated that he heard it directly. Ibn Khuzayma graded it sahih, no. 1724, as did Ibn Jarud, no. 291, and Hakim said it meets the criteria of Muslim, 1/281, and Dhahabi agreed with him.