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.

Imam (ع) said, "O Musayyab!" 

He said, "Yes. My Master!"

Imam (ع) said, "I will be going to Medina, the town of my grandfather, The Messenger of Allah (ص) in order to entrust my son Ali Reza (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 gaurd is with me at the door." 

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

Musayyab said, "No, my Master!"

Imam (ع) said, "Then wait.” He said, “O my Master! Please pray to Allah to make me steadfast/firm." 

Imam (ع) said, "O Allah make him steadfast/firm."

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

Musayyab added, "Then I heard Imam Kazim (عليه السلام) recite a dua 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: Uyoon al-Akhbar al-Redha, Shaikh Sadooq, 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]