اللَّهُمَّ أَنْتَ الْأَوَّلُ فَلَيْسَ قَبْلَكَ شَيْءٌ وَأَنْتَ الْآخِرُ فَلَيْسَ بَعْدَكَ شَيْءٌ.
O Allah, You are the First, and nothing is before You; You are the Last, and nothing is after You. (Ṣaḥīḥ Muslim, Book of Remembrance and Supplication, chapter on what to say before sleep)
Fa-laysa qablaka shayʾ explains true firstness; fa-laysa baʿdaka shayʾ explains true lastness.
No created existence shares Allah’s absolute beginninglessness and endlessness.