Sayar reported,

Some heads were brought from Iraq and set up at the gate of the mosque. Abu Umama came, entered the mosque, prayed two rakats, then went out to where the heads were. He looked at them, raised his head, and said three times, "The worst of those slain under the shade of heaven, and the best of those slain under the shade of heaven are those who killed them." Then he said three times, "Dogs of the Fire." Then he wept and turned away from them.Someone said to him, "Abu Umama, this statement of yours, when you said 'dogs of the Fire,' is it something you heard from the Messenger of Allah ﷺ, or something you say from your own opinion?"He replied, "Glory be to Allah, I would be exceedingly bold if that were so. Had I heard it from the Messenger of Allah ﷺ only once or twice," until he mentioned seven times, "I would have thought I should not relate it."The man asked, "Why did you weep?"He said, "Out of mercy for them," or, "From mercy toward them."

حدثنا أبو سعيد حدثنا عبد الله بن بحير حدثنا

سيار قال

جيء برءوس من قبل العراق فنصبت عند باب المسجد وجاء أبو أمامة فدخل المسجد فركع ركعتين ثم خرج إليهم فنظر إليهم فرفع رأسه فقال شر قتلى تحت ظل السماء ثلاثا وخير قتلى تحت ظل السماء من قتلوه وقال كلاب النار ثلاثا ثم إنه بكى ثم انصرف عنهم فقال له قائل يا أبا أمامة أرأيت هذا الحديث حيث قلت كلاب النار شيء سمعته من رسول الله ﷺ أو شيء تقوله برأيك قال سبحان الله إني إذا لجريء لو سمعته من رسول الله ﷺ مرة أو مرتين حتى ذكر سبعا لخلت أن لا أذكره فقال الرجل لأي شيء بكيت قال رحمة لهم أو من رحمتهم