Appears 6 times in the Quran.
17:101 وَلَقَدْ ءَاتَيْنَا مُوسَىٰ تِسْعَ ءَايَٰتٍۭ بَيِّنَٰتٍ فَسْـَٔلْ بَنِىٓ إِسْرَٰٓءِيلَ إِذْ جَآءَهُمْ فَقَالَ لَهُۥ فِرْعَوْنُ إِنِّى لَأَظُنُّكَ يَٰمُوسَىٰ مَسْحُورًا
And certainly We gave Musa nine clear signs; so ask the children of Israel. When he came to them, Firon said to him: Most surely I deem you, O Musa, to be a man deprived of reason.
And they remained in their cave three hundred years and (some) add (another) nine.
27:12 وَأَدْخِلْ يَدَكَ فِى جَيْبِكَ تَخْرُجْ بَيْضَآءَ مِنْ غَيْرِ سُوٓءٍ فِى تِسْعِ ءَايَٰتٍ إِلَىٰ فِرْعَوْنَ وَقَوْمِهِۦٓ إِنَّهُمْ كَانُوا۟ قَوْمًا فَٰسِقِينَ
And enter your hand into the opening of your bosom, it shall come forth white without evil; among nine signs to Firon and his people, surely they are a transgressing people.
And there were in the city nine persons who made mischief in the land and did not act aright.
38:23 إِنَّ هَٰذَآ أَخِى لَهُۥ تِسْعٌ وَتِسْعُونَ نَعْجَةً وَلِىَ نَعْجَةٌ وَٰحِدَةٌ فَقَالَ أَكْفِلْنِيهَا وَعَزَّنِى فِى ٱلْخِطَابِ
Surely this is my brother; he has ninety-nine ewes and I have a single ewe; but he said: Make it over to me, and he has prevailed against me in discourse.
Over it are nineteen.