Al-Adab Al-Mufrad, Book 38, Hadith 900 (English) ⓘ

'A'isha said, "I heard the Messenger of Allah, may Allah bless him and grant him peace, say, 'The arwah are a massed army. When they already know each other, they are friendly. When they do not know each other, they disagree.'"

حَدَّثَنَا عَبْدُ اللهِ قَالَ‏:‏ حَدَّثَنِي اللَّيْثُ، عَنْ يَحْيَى بْنِ سَعِيدٍ، عَنْ عَمْرَةَ، عَنْ عَائِشَةَ رَضِيَ اللَّهُ عَنْهَا قَالَتْ‏:‏ سَمِعْتُ النَّبِيَّ صلى الله عليه وسلم يَقُولُ‏:‏ الأرْوَاحُ جُنُودٌ مُجَنَّدَةٌ، فَمَا تَعَارَفَ مِنْهَا ائْتَلَفَ، وَمَا تَنَاكَرَ مِنْهَا اخْتَلَفَ‏.‏