Reference: al-Imaam Ibn Baaz – duroos wa mawaaqif wa ‘ibar – Page 71
Shaykh Ahmad ibn ‘Abdil-’Azeez ibn Baaz narrates:
The Shaykh used to call his children via the internal phone to wake them up for Salaat al-Fajr.
And when he called them, he would recite the [authentic and recommended] supplication:
«اَلْحَمْدُ لِلهِ الَّذِي أَحْيَانَا بَعْدَمَا أَمَاتَنَا وَ إِلَيْهِ النُّشُوْر»
«All praise is for Allaah who gave us life having taken it from us and unto Him is the resurrection»
As they were overcome by sleep, he would ask them to repeat this supplication until he felt sure they had woken up!
 al-Bukhaaree with Fat.hul-Baaree 11/113, and Muslim 4/2083.