1013. hadíth
وَ سَأَلَ عُبَيْدُ بْنُ زُرَارَةَ أَبَا عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ: عَنِ اَلرَّجُلِ يُصَلِّي اَلْغَدَاةَ رَكْعَةً وَ يَتَشَهَّدُ وَ يَنْصَرِفُ وَ يَذْهَبُ وَ يَجِيءُ ثُمَّ ذَكَرَ أَنَّهُ إِنَّمَا صَلَّى رَكْعَةً قَالَ «يُضِيفُ إِلَيْهَا رَكْعَةً.
Ubayd ibn Zurarah asked Imam Jafar ibn Muhammad Al-Sadiq (a.s) about a man who prays the Fajr prayer, offering one rak'ah, then makes the tashahhud (testification), turns away (ends the prayer), and leaves. After some time, he remembers that he only prayed one rak'ah. He asked what should he do. Imam (a.s) replied: "He should add another rak'ah to it”.