Sunan Abi Dawud 2597
سنن أبي داود#2597Sahihحَدَّثَنَا مُحَمَّدُ بْنُ كَثِيرٍ، أَخْبَرَنَا سُفْيَانُ، عَنْ أَبِي إِسْحَاقَ، عَنِ الْمُهَلَّبِ بْنِ أَبِي صُفْرَةَ، قَالَ أَخْبَرَنِي مَنْ، سَمِعَ النَّبِيَّ صلى الله عليه وسلم يَقُولُ " إِنْ بُيِّتُّمْ فَلْيَكُنْ شِعَارُكُمْ حم لاَ يُنْصَرُونَ " .
Narrated A man who heard the Prophet: Al-Muhallab ibn AbuSufrah said: A man who heard the Prophet (ﷺ) say: If the enemy attacks you at night, let your war cry be Ha-Mim. They will not be helped
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Al-AlbaniSahih
Muhammad Muhyi Al-Din Abdul HamidSahih
Zubair Ali ZaiSahih
In-book reference: 15:121