“And indeed this, your religion, is one religion” (Quran 23:52), meaning: one creed; that is: Islam.
Muhammad said: Whoever reads “wa-anna hadhihi” (and that this) with the fathah on the alif, the meaning is: because this is your religion.
﴿وَإِنَّ هَذِهِ أُمَّتُكُمْ أُمَّةً وَاحِدَةً﴾ أَيْ: مِلَّةً وَاحِدَةً؛ يَعْنِي: الْإِسْلَامَ.
قَالَ مُحَمَّدٌ: مَنْ قَرَأَ: ﴿وَأَنَّ هَذِهِ﴾ بِفَتْحِ الْأَلِفِ فَالْمَعْنَى: لِأَنَّ هَذِه أمتكُم.