In the introduction of the book The Allegories Volume 4, Imam Ahmed Alhasan a.s. says:
"ÙˆØ£Ù†Ø§ Ø§Ù„Ù…Ø¹Ø±ÙˆÙ ÙÙŠ Ø§Ù„Ø³Ù…Ø§Ø¡ Ù†Ø¬Ù…Ø© Ø§Ù„ØµØ¨Ø ÙˆØ¯Ø±Ø¹ Ø§Ù„Ø£Ù†Ø¨ÙŠØ§Ø¡ ÙˆØ§Ù„ØØµÙ† Ø§Ù„ØØµÙŠÙ†"
"ÙˆØ£Ù†Ø§ Ø§Ù„ØØ¬Ø± ÙˆØ§Ù„Ø±ÙƒÙ† Ø§Ù„ÙŠÙ…ÙŠÙ†"
"And I am the one who is known in the heavens as the morning star, and the armor of the prophets, and the invincible fortress". He also says: "and I am the stone, and I am the right corner".
Also Imam Ahmed Alhasan a.s. says that he is "The Strong Corner". In several of his communiques, he signed his name as follows:
"The remnant of the family of Muhammad (a.s)
The Strong Corner,
Vicegerent and Messenger of Imam Al-Mahdi (a.s)
To all the people
Supported by Gabriel, enforced by Michael, given victory by Israfel.
Offspring generation after generation and Allah is All-Hearing, All-Knowing.
So Imam Ahmed Alhasan a.s. is a lot of things but what I want to focus on now are the following:
The Armor of the Prophets
The Invicible Fortress
The Corner(which refers to both; "The Right Corner (the Iraqi corner of the Ka'ba which has the Black Stone in it), and "The Strong Corner (Supported by Gabriel, enforced by Michael, given victory by Israfel) )
Armor is "a defensive covering for body worn especially in combat". So the Prophets (a.s) would seek protection by Ahmed Alhasan a.s, since he was the armor of the Prophets.
Also we know from Imam Ahmed Alhasan a.s. that he said: "My father Imam Al-Mahdi (a.s.) ordered me to say these words: (I am a stone in the right hand of Ali ibn Abi Talib (a.s.) as he threw it one day to guide the ark of Noah (a.s.) and once to save Abraham from the fire of Nimrod, and another time to save Yunus from the belly of the whale, and spoke to Moses with it on the Toor (mountain Sinai) and made it a staff that split the sea, and an armor for David (a.s.), and shielded himself with it in Uhud, and folded it by his right in Siffin)"
So not only did the prophets protect themselves by Ahmed Alhasan a.s., but also Imam Ali a.s. shielded himself by Ahmed Alhasan a.s. in Uhud as mentioned in the above quote. Can we find other instances from the Imams a.s. where they protected themselves by Ahmed Alhasan a.s.?
In the Dua' of Ihtijab (veiling) by the Commander of the Believers Imam Ali a.s. he says: "I have veiled myself by the complete old light of the face of Allah, and I have fortified myself by the encompassing strong fortress of Allah"
Ø§ÙØØªÙŽØ¬ÙŽØ¨ØªÙ Ø¨ÙÙ†ÙˆØ±Ù ÙˆÙŽØ¬Ù‡Ù Ø§Ù„Ù„Ù‡Ù Ø§Ù„Ù‚ÙŽØ¯ÙŠÙ…Ù Ø§Ù„ÙƒØ§Ù…ÙÙ„ ÙˆØªÙŽØÙŽØµÙŽÙ‘Ù†ØªÙ Ø¨ØÙØµÙÙ†Ù Ø§Ù„Ù„Ù‡Ù Ø§Ù„Ù‚ÙŽÙˆÙÙŠÙ‘ Ø§Ù„Ø´Ù‘Ø§Ù…ÙÙ„Ù
And in Bihar Al-Anwar Volume 91, Page 328, in the amulet of Imam Musa Al-Kazim that he a.s. used when he was thrown to the lions:
"....and I have fortified myself from them by the invincible fortress, so they were not able to pass it ([or pass him]) nor were they able to pierce it ([or him]), so I took refuge in strong corner"
"ØªØØµÙ†Øª Ù…Ù†Ù‡Ù… Ø¨Ø§Ù„ØØµÙ† Ø§Ù„ØØµÙŠÙ†ØŒ ÙÙ…Ø§ Ø§Ø³Ø·Ø§Ø¹ÙˆØ§ Ø£Ù† ÙŠØ¸Ù‡Ø±ÙˆÙ‡ ÙˆÙ…Ø§ Ø§Ø³ØªØ·Ø§Ø¹ÙˆØ§ Ù„Ù‡ Ù†Ù‚Ø¨Ø§ØŒ ÙØ¢ÙˆÙŠØª Ø¥Ù„Ù‰ Ø±ÙƒÙ† Ø´Ø¯ÙŠØ¯"
Also you all know the Hadith of the Cloak, in it the Prophet sawas covered himself and his Ahlul Bayt a.s. by the Yamani Cloak. Later on we knew from Ahmed Alhasan a.s. that this Yamani cloak represents the Yamani Ahmed Alhasan. Rather, Prophet Muhammad sawas was cured after he covered himself by the Yamani cloak. About that Imam Ahmed Alhasan a.s said:
"Prophet Muhammad sawas was cured after he covered himself with the Yamani Cloak, and this cure is an indication to [the fact that] the fixing of the Muhammadan Islamic Religion after it was destroyed shall be completed by Allah through the Yamani" - Al-Jawab Al-Moneer (The Enlightening Answer Across the Ether) Question 487.
" Ø§Ù„Ø±Ø³ÙˆÙ„ Ù…ØÙ…Ø¯ <Øµ> Ø´ÙÙŠ Ø¨Ø¹Ø¯ Ø£Ù† ØªØºØ·Ù‰ Ø¨Ø§Ù„ÙƒØ³Ø§Ø¡ Ø§Ù„ÙŠÙ…Ø§Ù†ÙŠØŒ ÙˆÙ‡Ø°Ø§ Ø§Ù„Ø´ÙØ§Ø¡ Ø¥Ø´Ø§Ø±Ø© Ø¥Ù„Ù‰ Ø£Ù† ØµÙ„Ø§Ø Ø§Ù„Ø¯ÙŠÙ† Ø§Ù„Ø¥Ø³Ù„Ø§Ù…ÙŠ Ø§Ù„Ù…ØÙ…Ø¯ÙŠ Ø¨Ø¹Ø¯ Ø®Ø±Ø§Ø¨Ù‡ ÙŠØªÙ…Ù‡ Ø§Ù„Ù„Ù‡ Ø¨Ø§Ù„ÙŠÙ…Ø§Ù†ÙŠ " 
He a.s. also said:
" ÙˆØ§Ù„ÙƒØ³Ø§Ø¡ Ø§Ù„ÙŠÙ…Ø§Ù†ÙŠ Ø§Ù„Ø°ÙŠ Ø¨Ù‡ Ø´ÙØ§Ø¡ Ø§Ù„Ø®Ù…Ø³Ø© Ø£ØµØØ§Ø¨ Ø§Ù„ÙƒØ³Ø§Ø¡ (Ø¹) ÙØ¨Ù‡ ÙŠØ¬Ø¨Ø± Ø¶Ù„Ø¹ Ø§Ù„Ø²Ù‡Ø±Ø§Ø¡ (Ø¹) Ø§Ù„Ù…ÙƒØ³ÙˆØ± ÙˆÙŠØ³ÙƒÙ† Ø¯Ù… Ø§Ù„ØØ³ÙŠÙ† (Ø¹) Ø§Ù„Ø°ÙŠ ÙŠÙÙˆØ± ØŒ ÙˆØ¨Ù†ØµØ±Ù‡ ÙŠÙ†ØªØµØ±ÙˆÙ† ÙˆØ¨ØÙƒÙ…Ù‡ ÙŠØÙƒÙ…ÙˆÙ† " 
"And the Yamani cloak which by it is the cure of the five of the people of the cloak (a.s), by it Al-Zahraa's (a.s) broken rib is splint, and by it the boiling blood of Al-Hussein (a.s) calms down, and by its ([or his]) victory do they become victorious, and by its ([or his]) rule do they rule" - The Communique/Sermon of "An Advice to the Ansar of Imam Mahdi may Allah enable him on Earth" by Imam Ahmed Alhasan a.s.
The Yamani (a.s) is the Qa'im of the Family of Muhammad (a.s) and the one who will establish the Divine State of Justice and the one who will reveal the truth and reality of Muhammad sawas and his Family (a.s).
Imam Ahmed Alhasan (a.s) said in the Book of Monotheism:
(And this I shall leave for those whom understood and recognized that which I have provided, for verily, Imam Al Sadiq (pbuh) said: â€œIt is only upon us that we drop upon you the origin, while upon you is to stem out [from the origin].â€ And Imam Al Rida (pbuh) said: â€œUpon us is laying the foundation while upon you is stemming out/branching out.â€ )
More to come inshaAllah. Please share your thoughts and any valuable input which could eventually help us further understand the truth and reality of the Yamani a.s.
And peace, mercy, and blessings of Allah be upon you.