Only God possesses the power of intercession, just as He alone possesses mercy, forgiveness, the heavens and the earth.
الزمر : 44 قُلْ لِلَّهِ الشَّفاعَةُ جَميعاً لَهُ مُلْكُ السَّماواتِ وَ الْأَرْضِ ثُمَّ إِلَيْهِ تُرْجَعُونَ
Say, “All intercession belongs to God. The dominion of the heavens and the earth is His, and then you will all be returned to Him.”
No one can outstrip God in intercession, just as no one can surpass Him in love. A mother’s love for her child is a trust of divine love placed in her heart; intercession is likewise a manifestation of God, whatever form it may take. Its source is God.
Just as God bestows sovereignty upon whomever He wills, so too it is with intercession.
آلعمران : 26 قُلِ اللَّهُمَّ مالِكَ الْمُلْكِ تُؤْتِي الْمُلْكَ مَنْ تَشاءُ وَ تَنْزِعُ الْمُلْكَ مِمَّنْ تَشاءُ وَ تُعِزُّ مَنْ تَشاءُ وَ تُذِلُّ مَنْ تَشاءُ بِيَدِكَ الْخَيْرُ إِنَّكَ عَلى كُلِّ شَيْءٍ قَديرٌ
Say, “O God, Master of all sovereignty! You grant sovereignty to whomever You will and take it away from whomever You will. You exalt whomever You will and abase whomever You will. All goodness is in Your hand; You have power over all things.”
الأعراف : 156 وَ اكْتُبْ لَنا في هذِهِ الدُّنْيا حَسَنَةً وَ فِي الْآخِرَةِ إِنَّا هُدْنا إِلَيْكَ قالَ عَذابي أُصيبُ بِهِ مَنْ أَشاءُ وَ رَحْمَتي وَسِعَتْ كُلَّ شَيْءٍ فَسَأَكْتُبُها لِلَّذينَ يَتَّقُونَ وَ يُؤْتُونَ الزَّكاةَ وَ الَّذينَ هُمْ بِآياتِنا يُؤْمِنُونَ
And ordain for us what is good in this world and in the Hereafter; we have turned to You in repentance.” He said, “I inflict My punishment upon whomever I will, but My mercy encompasses all things. I shall ordain it for those who are mindful of God, give the prescribed alms, and believe in Our signs.”
God’s mercy encompasses all things. Yet the continuing, all-embracing reach of His special mercy is granted to those who are mindful of Him and give the prescribed alms.
By contrast, there are those who will despair of His mercy.
العنكبوت : 23 وَ الَّذينَ كَفَرُوا بِآياتِ اللَّهِ وَ لِقائِهِ أُولئِكَ يَئِسُوا مِنْ رَحْمَتي وَ أُولئِكَ لَهُمْ عَذابٌ أَليمٌ
Those who disbelieve in God’s signs and in their meeting with Him have despaired of My mercy; theirs will be a painful punishment.
The Infallibles (peace be upon them) are God’s mercy and blessings. One may benefit from them only by observing piety and God’s specific commands. The authority to grant someone the benefit of intercession rests with God; He bestows it upon whomever He wills. The Prophet and the Infallibles are manifestations of God’s mercy, and intercession is one branch of that mercy.
طه : 109 يَوْمَئِذٍ لا تَنْفَعُ الشَّفاعَةُ إِلاَّ مَنْ أَذِنَ لَهُ الرَّحْمنُ وَ رَضِيَ لَهُ قَوْلاً
On that Day, no one’s intercession will benefit anyone, except that of one to whom the All-Merciful has granted permission and whose word He approves.
سبأ : 23 وَ لا تَنْفَعُ الشَّفاعَةُ عِنْدَهُ إِلاَّ لِمَنْ أَذِنَ لَهُ حَتَّى إِذا فُزِّعَ عَنْ قُلُوبِهِمْ قالُوا ما ذا قالَ رَبُّكُمْ قالُوا الْحَقَّ وَ هُوَ الْعَلِيُّ الْكَبيرُ
No intercession before Him will avail, except for those whom He has permitted. (On that Day, all will be in turmoil) until the fear is lifted from their hearts and the command is issued. At that point, the guilty will ask their intercessors, “What has your Lord decreed?” They will reply, “The truth”—that is, He has spoken the truth and permitted intercession for those deserving of it. “He is the Most High, the Great.”
For a detailed discussion, see the booklet on intercession. God willing.