The Companion1 ʿAbdullāh ibn ʿUmar transmitted the Prophet's ﷺ words about sighting the moon. Here are short excerpts from two reports:
فَإِنْ غُمَّ عَلَيْكُمْ فَأَكْمِلُوا الْعِدَّةَ ثَلاَثِينَ (Sahih al-Bukhari: 1907)
Meaning: If the moon is obscured, complete thirty days.
فَإِنْ غُمَّ عَلَيْكُمْ فَاقْدِرُوا ثَلاَثِينَ (Sahih Muslim: 1080c)
Meaning: If the moon is obscured, count thirty days.
Some words differ, but the point here agrees: complete thirty days. Both reports also come from the same Companion, Ibn ʿUmar.
1. Companion (صحابی): someone who met the Prophet ﷺ as a believer and died upon faith.