919 - وَ ذَكَرَ اَلْفَضْلُ بْنُ شَاذَانَ عَنِ اَلرِّضَا عَلَيْهِ اَلسَّلاَمُ: «عِلَّةً أُخْرَى وَ هِيَ أَنَّهُ إِنَّمَا صَارَتِ اَلتَّكْبِيرَاتُ فِي أَوَّلِ اَلصَّلاَةِ سَبْعاً لِأَنَّ أَصْلَ اَلصَّلاَةِ رَكْعَتَانِ وَ اِسْتِفْتَاحَهُمَا بِسَبْعِ تَكْبِيرَاتٍ تَكْبِيرَةِ اَلاِفْتِتَاحِ وَ تَكْبِيرَةِ اَلرُّكُوعِ وَ تَكْبِيرَتَيِ اَلسَّجْدَتَيْنِ وَ تَكْبِيرَةِ اَلرُّكُوعِ فِي اَلثَّانِيَةِ وَ تَكْبِيرَتَيِ اَلسَّجْدَتَيْنِ فَإِذَا كَبَّرَ اَلْإِنْسَانُ فِي أَوَّلِ صَلاَةٍ سَبْعَ تَكْبِيرَاتٍ ثُمَّ نَسِيَ شَيْئاً مِنْ تَكْبِيرَاتِ اَلاِفْتِتَاحِ مِنْ بَعْدُ أَوْ سَهَا عَنْهَا لَمْ يَدْخُلْ عَلَيْهِ نَقْصٌ فِي صَلاَتِهِ».
Hadith.919 - Al-Fadl ibn Shadhan reported from Imam al-Rida 
:
"Another reason (for the seven takbirs) is that the original structure of the prayer is two Rak'ah (units), and the opening of these two Rak'ah with seven takbirs corresponds to the takbir for the opening, the takbir for bowing (Rukuh), and the two takbirs for the two prostrations (sujood) in the first rak’a, followed by the takbir for bowing in the second rak’a and the two takbirs for the two prostrations in the second rak’a.
Thus, if a person begins their prayer with seven takbirs and later forgets or misses one of the opening takbirs, it does not cause a deficiency in their prayer."
