Letter of Imam Musa Kazim (عليه السلام) from prison:

https://www.marefateahlebait.com/know-the-ahlul-bait/imam-moosa-kazim-leaves-aside-taqayyah 

Hadith 1:

عن عبد الله بن طاوس قال: قلت للرضا (ع): إن يحيى بن خالد سم أباك موسى بن جعفر (ع)؟ قال: نعم, سمه في ثلاثين رطبة.

Narrated that Abdullah bin Taoos asked Imam Ridha (ع), "Did Yahya bin Khaled poison your father Musa bin Jafar (ع)?"

Imam Ridha (ع) said, Yes, he poison Him with thirty dates."

[Source: Rijal al-Kashi, Pg. 604]

Hadith 2:

ثُمَّ إِنَّ سَيِّدَنَا مُوسَى(ع)دَعَا بِالْمُسَيَّبِ وَ ذَلِكَ قَبْلَ وَفَاتِهِ بِثَلَاثَةٍ أَيَّامٍ وَ كَانَ مُوَكَّلًا بِهِ فَقَالَ لَهُ يَا مُسَيَّبُ قَالَ لَبَّيْكَ يَا مَوْلَايَ قَالَ إِنِّي ظَاعِنٌ فِي هَذِهِ اللَّيْلَةِ إِلَى الْمَدِينَةِ مَدِينَةِ جَدِّي رَسُولِ اللَّهِ (ص) لِأَعْهَدَ إِلَى عَلِيٍّ ابْنِي‏ مَا عَهِدَهُ إِلَيَّ أَبِي وَ أَجْعَلَهُ وَصِيِّي وَ خَلِيفَتِي وَ آمُرَهُ أَمْرِي قَالَ الْمُسَيَّبُ فَقُلْتُ يَا مَوْلَايَ كَيْفَ تَأْمُرُنِي أَنْ أَفْتَحَ لَكَ الْأَبْوَابَ وَ أَقْفَالَهَا وَ الْحَرَسُ مَعِي عَلَى الْأَبْوَابِ فَقَالَ يَا مُسَيَّبُ ضَعُفَ يَقِينُكَ بِاللَّهِ عَزَّ وَ جَلَّ وَ فِينَا قُلْتُ لَا يَا سَيِّدِي قَالَ فَمَهْ قُلْتُ يَا سَيِّدِي ادْعُ اللَّهَ أَنْ يُثَبِّتَنِي فَقَالَ اللَّهُمَّ ثَبِّتْهُ ثُمَّ قَالَ إِنِّي أَدْعُو اللَّهَ عَزَّ وَ جَلَّ بِاسْمِهِ الْعَظِيمِ الَّذِي دَعَا آصَفُ حَتَّى جَاءَ بِسَرِيرِ بِلْقِيسَ وَ وَضَعَهُ بَيْنَ يَدَيْ سُلَيْمَانَ قَبْلَ ارْتِدَادِ طَرْفِهِ إِلَيْهِ حَتَّى يَجْمَعَ بَيْنِي وَ بَيْنَ ابْنِي عَلِيٍّ بِالْمَدِينَةِ قَالَ الْمُسَيَّبُ فَسَمِعْتُهُ(ع)يَدْعُو فَفَقَدْتُهُ عَنْ مُصَلَّاهُ فَلَمْ أَزَلْ قَائِماً عَلَى قَدَمَيَّ حَتَّى رَأَيْتُهُ قَدْ عَادَ إِلَى مَكَانِهِ وَ أَعَادَ الْحَدِيدَ إِلَى رِجْلَيْهِ فَخَرَرْتُ لِلَّهِ سَاجِداً لِوَجْهِي شُكْراً عَلَى مَا أَنْعَمَ بِهِ عَلَيَّ مِنْ مَعْرِفَتِهِ

Part of a long narration on the Martyrdom of Imam Musa Kazim (عليه السلام):

Then our Master Imam Musa Kazim (عليه السلام) called in Musayyab three days /before his death. Musayyab was his guard.

The Imam said, "O Musayyab!" 

He said, "Yes. My Master!"

The Imam said, "I will be going to Medina, the town of my grandfather, The Messenger of Allah (صلى الله عليه وآله) in order to entrust my son Ali Ridha (عليه السلام) according to what my father had entrusted to me, and establish him as my Trustee and Successor, and deliver my orders to him."

Musayyab said, "O my Master! How do you order me to open the doors for you while the guard is with me at the door." 

The Imam said, "O Musayyab! Your belief in Allah (عز وجل) and in Us is weak."

Musayyab said, "No, my Master!"

Imam said, "Then what." 

Musayyab said, "O my Master! Please pray to Allah to make me steadfast/firm." 

The Imam said, "O Allah make him steadfast/firm."

Then the Imam said, "I ask Allah (عز وجل) by His Great Name - by which Asif had invoked Him, and brought the throne of Bilqis [queen of Sheba] there and placed it in front of Sulayman before the wink of an eye - to bring Me and my son Ali Ridha (عليه السلام) together in Medina."

Then Musayyab said, "Then I heard Imam Kazim (عليه السلام) recite a supplication and suddenly He was no longer on His prayer mat. As I was standing there, I saw him reappear there again, and tie the chains to his own feet. At that time I fell in prostration to Allah to thank Him for his blessing upon me with the Imams recognition [Marefat]."

[Source: Uyun Akhbar al-Redha, Shaikh Saduq, Vol. 1, Pg. 102-103]

Hadith 3:

أحمد بن مهران - رحمه الله - عن محمد بن علي، عن سيف بن عميرة، عن إسحاق ابن عمار قال: سمعت العبد الصالح ينعى إلى رجل نفسه، فقلت في نفسي: وإنه ليعلم متى يموت الرجل من شيعته!؟ فالتفت إلي شبه المغضب، فقال: يا إسحاق قد كان رشيد الهجري يعلم علم المنايا والبلايا والامام أولى بعلم ذلك

Narrated from Ishaq ibn Ammar who has said the following,

"Once I heard the pious servant (i.e. Imam Kazim (عليه السلام) informing a person of his death. 

So I said to myself, "Surely He knows when a man from his followers will die?" 

The Imam (عليه السلام) turned to me, as if he was angry, and said, "O Ishaq, Rushaid al-Hijri had the knowledge of death and calamities, and the Imam is more worthy of knowing that."

[Source: al-Kafi, Vol. 1, Pg. 484]

Hadith 4:

عَلِيُّ بْنُ إِبْرَاهِيمَ رَفَعَهُ عَنْ مُحَمَّدِ بْنِ مُسْلِمٍ قَالَ دَخَلَ أَبُو حَنِيفَةَ عَلَى أَبِي عَبْدِ الله (عَلَيْهِ الْسَّلام) فَقَالَ لَهُ رَأَيْتُ ابْنَكَ مُوسَى (عَلَيْهِ الْسَّلام) يُصَلِّي وَالنَّاسُ يَمُرُّونَ بَيْنَ يَدَيْهِ فَلاَ يَنْهَاهُمْ وَفِيهِ مَا فِيهِ فَقَالَ أَبُو عَبْدِ الله (عَلَيْهِ الْسَّلام) ادْعُوا لِي مُوسَى فَدُعِيَ فَقَالَ لَهُ يَا بُنَيَّ إِنَّ أَبَا حَنِيفَةَ يَذْكُرُ أَنَّكَ كُنْتَ تُصَلِّي وَالنَّاسُ يَمُرُّونَ بَيْنَ يَدَيْكَ فَلَمْ تَنْهَهُمْ فَقَالَ نَعَمْ يَا أَبَةِ إِنَّ الَّذِي كُنْتُ أُصَلِّي لَهُ كَانَ أَقْرَبَ إِلَيَّ مِنْهُمْ يَقُولُ الله عَزَّ وَجَلَّ وَنَحْنُ أَقْرَبُ إِلَيْهِ مِنْ حَبْلِ الْوَرِيدِ قَالَ فَضَمَّهُ أَبُو عَبْدِ الله (عَلَيْهِ الْسَّلام) إِلَى نَفْسِهِ ثُمَّ قَالَ يَا بُنَيَّ بِأَبِي أَنْتَ وَأُمِّي يَا مُوَدَّعَ الأسْرَارِ

Narrated that Abu Hanifa entered upon Abu Abd-Allah Imam Jafar al-Sadiq (عليه السلام) and said to him:

"I saw your son Musa [al-Kazim] (عليه السلام) praying while people were passing in front of him, and he did not stop them. And in this, there is what there is (i.e., it is objectionable)."

Imam Sadiq (عليه السلام) said to him: "O my son, Abu Hanifa mentions that you were praying while people were passing in front of you, and you did not stop them."

Imam Musa Kazim (عليه السلام) said: "Yes, father. The One to Whom I was praying was closer to me than they were. Allah (عز وجل) says: 'And We are closer to him than [his] jugular vein.' (50:16)"

Then Imam Sadiq (عليه السلام) embraced him and said: "O my son—may my father and mother be sacrificed for you - O reservoir of secrets."

[Source: al-Kafi, Vol. 3, Book. 4, Ch. 14, Hadith. 4]