Man Lā Yaḥḍuruh al-Faqīh

Hadith 997
worship
999 - وَ سَأَلَ اَلْحَلَبِيُّ أَبَا عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ: عَنْ رَجُلٍ نَسِيَ أَنْ يُكَبِّرَ حَتَّى دَخَلَ فِي اَلصَّلاَةِ فَقَالَ «أَ لَيْسَ كَانَ فِي نِيَّتِهِ أَنْ يُكَبِّرَ» قَالَ نَعَمْ قَالَ «فَلْيَمْضِ فِي صَلاَتِهِ.
Hadith.999 - The Halabi asked Imam Jafar ibn Muhammad Al-Sadiq (as) about a man who forgot to say the Takbir (the opening Takbir) until he had entered the prayer. Imam (as) said: "Was it not in his intention to say the Takbir?" He replied: "Yes." Imam (as) said: "Then let him continue with his prayer."
Source: Shaykh Muḥammad b. ʿAlī al-Ṣaduq