So when the night covered him [with darkness], he saw a star. (6:76)

﴿فَلَمَّا جَنَّ عَلَيْهِ اللَّيْلُ رَأَىٰ كَوْكَبًا ۖ قَالَ هَٰذَا رَبِّي ۖ فَلَمَّا أَفَلَ قَالَ لَا أُحِبُّ الْآفِلِينَ﴾
[ الأنعام: 76]

6:76 So when the night covered him [with darkness], he saw a star. He said, "This is my lord." But when it set, he said, "I like not those that disappear."

When the darkness of the night came over Abraham, he began to debate with his people in order to bring them from idolatry to monotheism.
His people used to worship the stars, so when he saw a star he said, ‘This is my Lord’, with the aim of convincing his people.
When the star disappeared, he said, ‘I do not like that which disappears, because the true God is always present and never disappears’.
The belief of his people was that gods do not go away and disappear, so he used this same belief of theirs as an argument against them.

When the night covered him over with darkness he saw a star. He said: "This is my lord." But when it set, he said: "I like not those that set."

phonetic Transliteration

Falamma janna AAalayhi allaylu raa kawkaban qala hatha rabbee falamma afala qala la ohibbu alafileena

Abdullah Yusuf Ali - Translation

When the night covered him over, He saw a star: He said: "This is my Lord." But when it set, He said: "I love not those that set."

Safi-ur-Rahman al-Mubarakpuri

When the night overcame him he saw a Kawkab. He said: "This is my lord." But when it Afala, he said: "I like not those that set."

Page 137 English transliteration