Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
quran:86:3

It is the piercing star -  

The piercing, the brilliant, because of its piercing the darkness with its light, star!, meaning ˹the constellation˺ Pleiades; or ˹it refers to˺ all stars (the response to the oath ˹follows˺):
القرآن:٨٦:٣

النَّجْمُ الثَّاقِبُ  

{النجم} أي الثريا أو كل نجم {الثاقب} المضيء لثقبه الظلام بضوئه وجواب القسم.