The Quran

إِذ جاءوكُم مِن فَوقِكُم وَمِن أَسفَلَ مِنكُم وَإِذ زاغَتِ الأَبصارُ وَبَلَغَتِ القُلوبُ الحَناجِرَ وَتَظُنّونَ بِاللَّهِ الظُّنونا

Ali Unal

(Remember) when they came upon you from above you (from the east), and from below you (from the west), and when (your) eyes turned dull, and (your) hearts came up to the throats, and (those of weak faith among) you were harboring vain thoughts about God.¹

Some thought that the unbelievers would be victorious and invade Madīnah; others that Islam would be wiped out; and still others that pre-Islamic unbelief would come back, or entertained other negative thoughts.