"What prevented you that you did not prostrate when I commanded you?" (the verse).
Muhammad said: "That you do not prostrate" (alla tasjuda) means: that you prostrate, and the "la" is for emphasis.
﴿مَا مَنَعَكَ أَلَّا تَسْجُدَ إِذْ أَمرتك﴾ الْآيَةَ.
قَالَ محمدٌ: (أَلَّا تَسْجُدَ) مَعْنَاهُ: أَن تسْجد، و (لَا) مُؤَكدَة.
