This hadith is about the time of offering Salat al-Layl or the night prayer. It was narrated by An-Nu'man ibn Bashir that Prophet Muhammad (PBUH) used to offer this prayer at a specific time which was when the moon went down on its third night. This hadith teaches us that we should be punctual in our prayers and should not delay them unnecessarily. We should also try to pray at a fixed time every day so that it becomes a habit and we can reap maximum benefit from it.