يقع العلم بخبرهم
Translation: Whose report gives rise to reliable knowledge.
Quduri completes the condition with yaqaʿ al-ʿilm bi-khabarihim: the group’s report must yield sufficient reliable knowledge of the sighting. Numbers alone are not the whole point; credible collective evidence matters.
The closing words clarify what kind of group is intended under a clear sky: one whose report can establish the matter with the required assurance.