حَدَّثَنَا الْحَاكِمُ أَبُو عَلِيٍّ الْحُسَيْنُ بْنُ أَحْمَدَ الْبَيْهَقِيُّ قَالَ حَدَّثَنِي مُحَمَّدُ بْنُ يَحْيَى الصَّوْلِيُّ قَالَ‌ يُحْكَى عَنِ الرِّضَا(ع)خَبَرٌ مُخْتَلِفُ الْأَلْفَاظِ لَمْ تَقَعْ لِي رِوَايَتُهُ بِإِسْنَادٍ أَعْمَلُ عَلَيْهِ وَ قَدِ اخْتَلَفَتْ أَلْفَاظُ مَنْ رَوَاهُ إِلَّا أَنِّي سَآتِي بِهِ وَ بِمَعَانِيهِ وَ إِنِ اخْتَلَفَتْ أَلْفَاظُهُ كَانَ الْمَأْمُونُ فِي بَاطِنِهِ يُحِبُّ سَقَطَاتِ الرِّضَا(ع)وَ أَنْ يَعْلُوَهُ الْمُحْتَجُّ وَ إِنْ أَظْهَرَ غَيْرَ ذَلِكَ فَاجْتَمَعَ عِنْدَهُ الْفُقَهَاءُ وَ الْمُتَكَلِّمُونَ فَدَسَّ إِلَيْهِمْ أَنْ نَاظِرُوهُ فِي الْإِمَامَةِ فَقَالَ لَهُمُ الرِّضَا(ع)اقْتَصِرُوا عَلَى وَاحِدٍ مِنْكُمْ يَلْزَمُكُمْ مَا يَلْزَمُهُ فَرَضُوا بِرَجُلٍ يُعْرَفُ بِيَحْيَى بْنِ الضَّحَّاكِ السَّمَرْقَنْدِيِّ وَ لَمْ يَكُنْ بِخُرَاسَانَ مِثْلُهُ فَقَالَ لَهُ الرِّضَا(ع)يَا يَحْيَى سَلْ عَمَّا شِئْتَ فَقَالَ نَتَكَلَّمُ فِي الْإِمَامَةِ كَيْفَ ادَّعَيْتَ لِمَنْ لَمْ يَؤُمَّ وَ تَرَكْتَ مَنْ أَمَّ وَ وَقَعَ الرِّضَا بِهِ فَقَالَ لَهُ يَا يَحْيَى أَخْبِرْنِي عَمَّنْ صَدَقَ كَاذِباً عَلَى نَفْسِهِ أَوْ كَذَبَ صَادِقاً عَلَى نَفْسِهِ أَ يَكُونُ مُحِقّاً مُصِيباً أَوْ مُبْطِلًا مُخْطِئاً فَسَكَتَ يَحْيَى فَقَالَ لَهُ الْمَأْمُونُ أَجِبْهُ فَقَالَ يُعْفِينِي أَمِيرُ الْمُؤْمِنِينَ مِنْ جَوَابِهِ فَقَالَ الْمَأْمُونُ يَا أَبَا الْحَسَنِ عَرِّفْنَا الْغَرَضَ فِي هَذِهِ الْمَسْأَلَةِ فَقَالَ لَا بُدَّ لِيَحْيَى مِنْ أَنْ يُخْبِرَ عَنْ أَئِمَّتِهِ أَنَّهُمْ كَذَبُوا عَلَى أَنْفُسِهِمْ أَوْ صَدَقُوا فَإِنْ زَعَمَ أَنَّهُمْ كَذَبُوا فَلَا أَمَانَةَ لِكَذَّابٍ وَ إِنْ زَعَمَ أَنَّهُمْ صَدَقُوا فَقَدْ قَالَ أَوَّلُهُمْ وُلِّيتُكُمْ وَ لَسْتُ بِخَيْرِكُمْ وَ قَالَ تَالِيهِ كَانَتْ بَيْعَتُهُ فَلْتَةً فَمَنْ عَادَ لِمِثْلِهَا فَاقْتُلُوهُ فَوَ اللَّهِ مَا رَضِيَ لِمَنْ فَعَلَ مِثْلَ فِعْلِهِمْ إِلَّا بِالْقَتْلِ فَمَنْ لَمْ يَكُنْ بِخَيْرِ النَّاسِ وَ الْخَيْرِيَّةُ لَا تَقَعُ إِلَّا بِنُعُوتٍ مِنْهَا الْعِلْمُ وَ مِنْهَا الْجِهَادُ وَ مِنْهَا سَائِرُ الْفَضَائِلِ وَ لَيْسَتْ فِيهِ وَ مَنْ كَانَتْ بَيْعَتُهُ‌ فَلْتَةً يَجِبُ الْقَتْلُ عَلَى مَنْ فَعَلَ مِثْلَهَا كَيْفَ يُقْبَلُ عَهْدُهُ إِلَى غَيْرِهِ وَ هَذِهِ صُورَتُهُ ثُمَّ يَقُولُ عَلَى الْمِنْبَرِ إِنَّ لِي شَيْطَاناً يَعْتَرِينِي فَإِذَا مَالَ بِي فَقَوِّمُونِي وَ إِذَا أَخْطَأْتُ فَأَرْشِدُونِي فَلَيْسُوا أَئِمَّةً بِقَوْلِهِمْ إِنْ صَدَقُوا أَوْ كَذَبُوا فَمَا عِنْدَ يَحْيَى فِي هَذَا جَوَابٌ فَعَجِبَ الْمَأْمُونُ مِنْ كَلَامِهِ وَ قَالَ يَا أَبَا الْحَسَنِ مَا فِي الْأَرْضِ مَنْ يُحْسِنُ هَذَا سِوَاكَ‌

Narrated that, al-Mamun would secretly love for Imam al-Rida (عليه السلام) to commit mistakes/errors and for a debater to overcome Him, although Mamun made a show of the opposite in public.

Many jurists and theologians were once gathered in his (i.e. al-Mamun’s) presence so he (i.e, al-Mamun) sent them a private message (saying), "Debate him in Imamah."

Imam al-Rida (عليه السلام) said to them, "Limit yourself to one (representative) among you who is bound by what you are bound (i.e. with whom you share a common stance/belief)"

They chose a man who was known as Yahya bin al-Dahhak al-Samarqandi and there was no one in all of Khurasan who was his equal.

Imam al-Rida (عليه السلام) said to him, "Ask whatever you wish O Yahya."

He (i.e., Yahya) said, "We should speak on Imamah. On what basis did you uphold (the Imamah of) one who did not get to rule (i.e. Ali ibn Abi Ṭalib ع) and discard the one who actually came to rule and gained acceptance (i.e. Abu Bakr)?"

Imam al-Rida (عليه السلام) said to him, “Inform me, O Yahya, about a person who believes in a man who is lying about himself, or disbelieves in a man who is speaking the truth about himself – will such a one be correct in doing so or mistaken?”

Yahya kept silent.

al-Mamun said to him, "Answer him"

Yahya said, "The Commander of the Faithful should excuse me from answering"

Yahya had glimpsed where the Imam was going with this and pulled out of the debate, but al-Mamun said, “Inform us O Aba al-Hasan (i.e. al-Rida ع) – the intention behind this question.”

Imam al-Rida (عليه السلام) said, 

Yahya has no option but to declare on behalf of his Imams either that they lied about themselves or spoke the truth.

So, if he asserts that they lied then there is no trusting a liar!

And if he asserts that they spoke the truth then the first one of them (i.e. Abu Bakr) had said, 'I have been made a ruler over you while I am not the best of you' and the one who followed him (i.e. Umar) had said 'The pledge of allegiance to him (i.e. Abu Bakr) was abrupt (sudden or slip or lapse), so the one who repeats a thing like it then kill him!’' By Allah he was not satisfied with any other punishment for the one who acts in the way they themselves acted except to be put to death!

So the one who is not the best among people – and being the best depends on certain criteria, such as knowledge, Jihad, and other merits and he (i.e. Abu Bakr) did not possess them – and the one whose pledge of allegiance was abrupt, death being the only punishment for whoever repeats something similar to it, how can his transfer of power to another be accepted when his own status is like this?!      

Then he (i.e. Abu Bakr) says on the pulpit, 'I have a devil who possesses me, so if I am made to incline then set me aright, and if I make a mistake then correct me.'

So they are not Imams by their own words, whether they were speaking the truth or lying, and Yahya does not have an answer to this!

al-Mamun was much impressed by the Imams words and said, "There is no one on Earth who is better at this than you O Aba al-Hasan (عليه السلام)"

[Source: Uyun Akhbar al-Rida, Vol. 2, Pgs. 231-232]