Al-Adab Al-Mufrad, Hadith 900 ⓘ
'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.
also referenced under: Book 38, Hadith 13 (In-Book) & Book 38, Hadith 900 (English)