Chapter on the Detailed Explanation of Prayer, Including the Obligatory and Recommended, and What is Permissible and Not Permissible.

Tahdhīb al-Aḥkām|Volume 2|Book 1|Chapter 9

Tahdhīb al-Aḥkām

Volume 2, Book 1, Chapter 9

Chapter on the Detailed Explanation of Prayer, Including the Obligatory and Recommended, and What is Permissible and Not Permissible.

Hadith #15

وَ عَنْهُ عَنِ اِبْنِ أَبِي عُمَيْرٍ عَنْ جَمِيلٍ عَنْ زُرَارَةَ قَالَ: سَأَلْتُ أَبَا جَعْفَرٍ عَلَيْهِ اَلسَّلاَمُ عَنِ اَلرَّجُلِ يَنْسَى تَكْبِيرَةَ اَلاِفْتِتَاحِ قَالَ« يُعِيدُ»

And from him, from Ibn Abi ‘Umayr from Jamil from Zurarah, who said: I asked Abu Ja’far about a man who forgets the Takbirat al-Iftitah (opening Takbir). Imam said: "He must repeat (the prayer)."

Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 2, p. 152