554 - وَقَالَ عُمَرُ بْنُ يَزِيدَ: قُلْتُ لِأَبِي عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ يُصَلَّى عَنِ اَلْمَيِّتِ فَقَالَ «نَعَمْ حَتَّى إِنَّهُ لَيَكُونُ فِي ضِيقٍ فَيُوَسِّعُ اَللَّهُ عَلَيْهِ ذَلِكَ اَلضِّيقَ ثُمَّ يُؤْتَى فَيُقَالُ لَهُ خُفِّفَ عَنْكَ هَذَا اَلضِّيقُ بِصَلاَةِ فُلاَنٍ أَخِيكَ عَنْكَ» قَالَ فَقُلْتُ لَهُ فَأُشْرِكُ بَيْنَ رَجُلَيْنِ فِي رَكْعَتَيْنِ قَالَ «نَعَمْ» فَقَالَ عَلَيْهِ اَلسَّلاَمُ «إِنَّ اَلْمَيِّتَ لَيَفْرَحُ بِالتَّرَحُّمِ عَلَيْهِ وَ اَلاِسْتِغْفَارِ لَهُ كَمَا يَفْرَحُ اَلْحَيُّ بِالْهَدِيَّةِ تُهْدَى إِلَيْهِ. ويجوز أن يجعل الرجل حجته أو عمرته أو بعض صلاته أو بعض طوافه لبعض أوله وهو ميت وينتفع به حتى أنه ليكون مسخوطا عليه فيغفر له، ويكون مضيقا عليه فيوسع له ، ويعلم الميت بذلك، ولو أن رجلا فعل ذلك عن ناصب لخفف عنه ، والبر والصلة والحج يجعل للميت والحي، فأما الصلاة فلا تجوز عن الحي.
Hadith.554 - Omar ibn Yazid said: I asked Imam Jafar ibn Muhammad Al-Sadiq 
whether it is permissible to pray on behalf of a deceased person.
Imam replied: "Yes, even to the extent that if the deceased is in difficulty, Allah (swt) will alleviate that difficulty through the prayer of his brother for him. Then it is said to the deceased, 'Your difficulty has been eased by the prayer of such-and-such, your brother, on your behalf.'"
I then asked: "Can I include two people in one set of two units of prayer?"
Imam replied: "Yes."
He also said: "The deceased rejoices in mercy and forgiveness offered on his behalf just as the living person rejoices in a gift given to him."
[AL SADUQ]
It is permissible to perform pilgrimage (Hajj or Umrah), prayer, or circumambulation (Tawaf) on behalf of a deceased person, and they benefit from it—even if the deceased was under divine displeasure, they may be forgiven or have their hardship relieved through such actions. The deceased is made aware of these acts. Even performing these acts for an adversary (nāṣib) could lessen their burden. Acts of piety, connection, and Hajj can be performed for both the living and the dead, but prayer on behalf of a living person is not permitted.
