Straight rows or divided hearts

Crooked rows lead to Allah putting differences between the hearts.

Narrated by an-Nu'man ibn Bashir

You will straighten your rows, or Allah will cause differences between your faces.

Sahih al-Bukhari 717, Sahih Muslim 436

What this hadith teaches

The outward line affects the inner state: when shoulders are not level, hearts drift apart.

Reference and grade

Grade
Sahih: agreed upon by al-Bukhari and Muslim
Narrator
an-Nu'man ibn Bashir

The hadith in Arabic نص الحديث

لَتُسَوُّنَّ صُفُوفَكُمْ أَوْ لَيُخَالِفَنَّ اللَّهُ بَيْنَ وُجُوهِكُمْ

Arabic text of Sahih al-Bukhari 717, as given on sunnah.com.