1. Ibn Qudama Hanbali and other great hanabila took part in the battle of Hattin and liberation of al quds with Sultan salah ud din.
Al-Hafiz Ibn Kathir said, in his biography of the righteous shaykh Abu ‘Umar al-Maqdisi, the brother of Ibn Qudama Hanbali.
وكان هو وأخوه وابن خالهم الحافظ عبد الغني وأخوه الشيخ العماد: لا ينقطعون عن غَزاة يخرج فيها الملك صلاح الدين إلى بلاد الفرنج، وقد حضروا معه فتح القدس الشريف وغيرها
“Abu Umar, his brother Ibn Qudama, their maternal cousin Al-Hafiz Abdul-Ghani, and his brother Shaykh Al-Imad consistently accompanied Sultan Salah ad-Din on military campaigns against the Franks. They fought alongside him during the conquest of Jerusalem (Al-Quds) and participated in numerous other battles.”
(Al-Bidayah wa’n-Nihayah 17/21).
2. It is said he is same Abu Umar, when Mongols attacked and some poet encouraged to take the shelter on his grave,
Ibn Taymiyah said:
، وقال بعض الشعراء:
يا خائفين من التتر … لوذوا بقبر أبي عمر
أو قال:
عوذوا بقبر أبي عمر … ينجيكم من الضرر
فقلت لهم: هؤلاء الذين تستغيثون بهم لو كانوا معكم في القتال لانهزموا.
Some poets said: Oh, those who fear the Tatars… seek refuge in the grave of Abu Umar, or he said: seek protection in the grave of Abu Umar… it will save you from harm.
So I said to them: These people you’re seeking help from, if they were with you in battle, they would flee. (Meaning going to graves and asking help will not be a reason of victory, victory is due to doing Jihad).
Kitab al Istigatha fe Radd al Bakri 1/412, 413.
3. Abdul Aziz bin abdur Rahman bin saeed said:
كذلك شهد الموفق آخر الحروب الصليبية في عهد صلاح الدين الذي كسر شوكة الصليبين في «حطين ) وحرر « القدس ) من أيديهم في رجب عام ٥٨٣ه
Likewise al Muwaffaq witnessed the last of the Crusade wars in the leadership of Salah ud din who shattered them in Hattin and liberated al Quds ..
ابن قدامة وآثاره الأصولية عبد العزيز بن عبد الرحمن السعيد ومعه روضة الناظر لابن قدامة page 96
4. Arabic wikipedia states
ولما زحف صلاح الدين الأيوبي جيوش الإسلام لتحرير فلسطين في شهر المحرم سنة 583 هـ/ 1187م كان الشيخ ابن قدامة في مقدمة تلك الجيوش، وشرفه الله بالمشاركة في حصار الكرك، وعكا، وفتح طبرية، ومعركة حطين قرب النبي شعيب في 25 من شهر ربيع الثاني حيث أُسر ملك الإفرنج جيفري، وأميرهم أرناط، وشارك الشيخ ابن قدامة مع صلاح الدين في تحرير طبريا وعكا والناصرة وقيسارية وصفورية وتبنين وصيدا، وتحرير بيروت في 29 جمادى الأولى، وتحرير عسقلان، وفتح القدس يوم الجمعة 27 من شهر رجب الفرد، ونصب فيها المنبر الذي أرسله نور الدين بن محمود زنكي، وكان الشيخ ابن قدامة في الثانية والأربعين من عمره، وكان يقضي وقته بين التدريس والجهاد في سبيل الله، ولما بلغ التاسعة والسبعين من عمره وافاه الأجل يوم عيد الفطر المبارك سنة 620 هـ/ 1223 م، ودفن في مغارة التوبة بمدينة دمشق.
When Salah ad-Din al-Ayyubi led the armies of Islam to liberate Palestine in the month of Muharram 583 AH/1187 CE, Sheikh Ibn Qudamah was at the forefront of those armies. God honored him with the opportunity to participate in the siege of Karak and Acre, the conquest of Tiberias, and the Battle of Hattin near Nabi Shu’aib on the 25th of Rabi’ al-Thani, where King Geoffrey of the Franks and their prince, Arnault, were captured. Sheikh Ibn Qudamah participated with Salah ad-Din in the liberation of Tiberias, Acre, Nazareth, Caesarea, Safed, Tibnin, Sidon, and Beirut on the 29th of Jumada al-Ula, and the liberation of Ascalon and the conquest of Jerusalem on Friday, the 27th of Rajab al-Fard. The pulpit sent by Nur ad-Din Zengi was installed there, and Sheikh Ibn Qudamah was forty-two years old at the time. He spent his time between teaching and jihad in the way of Allah. When he reached the age of seventy-nine, he died on the day of Eid al-Fitr in the year 620 AH/1223 CE, and was buried in the Cave of Repentance in the city of Damascus. (End quote Wikipedia)
5. Did you know teacher of Ibn Jawzi, Ibn Aqil Hanbali asked the king to do Jihad against crusaders when they took control of Bayt al maqdas and killed 60k Muslims. But nothing happened.
Ibn Kathir quoted Ibn al Jawzi saying::
وندب الخليفة الفقهاء إلى الخروج إلى البلاد ليحرضوا الملوك على الجهاد، فخرج ابن عقيل وغير واحد من أعيان الفقهاء فساروا في الناس فلم يفد ذلك شيئا، فإنا لله وإنا إليه راجعون.
The Caliph asked the fuqaha to go to the cities so that they may ask the Muslim kings to do Jihad, Ibn Aqil (Hanbali) and other jurists went but nothing happened. Inna Lillah wa inna Iliyhe Rajioon. [albidaya wal Nihaya vol 12 under 492 h]
They ruled it until Ayyubi destroyed them after more than 90 years. This shows when Muslim kings were extremely divided and feared the numbers of crusaders, they took control of Bayt al Maqdas.
6. When Salah ud din liberated Bayt al Maqdas.
Ibn Shaddad the teacher of Salah ud din wrote:
قصده العلماء من مصر ومن الشام بحيث لم يتخلف معروف من الحضور، وارتفعت الأصوات بالضجيج والدعاء والتهليل والتكبير، وخطب فيه
Scholars came to join him , both from Egypt and from Syria ; there was not a single well-known scholar but came to the camp. Every voice was raised in shouts, calling upon Allah, and proclaiming His unity and power.
[Seerah Salah ud din by his teacher Ibn Shaddad 1/54]7. Hanbali scholars along with others united against kuffar.
Ibn Kathir recorded the actions of a Roman king who massacred thousands of Muslims, prompting scholars from all sects to issue a fatwa for combat against them and urging the ruler to take action:
وفيها: اجتمع الفقيه أبو بكر الرازي الحنفي وأبو الحسن علي بن عيسى الرماني وابن الدقاق الحنبلي بعز الدولة بختيار بن بويه وحرضوه على غزو الروم، فبعث جيشا لقتالهم فأظفره الله بهم، وقتلوا منهم خلقا كثيرا وبعثوا برؤوسهم إلى بغداد فسكنت أنفس الناس.
This year: The jurist Abu Bakr Al-Razi Al-Hanafi, Abu Al-Hasan Ali Bin Isa Al-Ramani (al Mutazili) and Ibn Al-Daqaq Al-Hanbali met with Izz al Dawla Bakhtiar Bin Buyh, and incited him to invade the Romans. So he sent an army to fight them and Allah granted victory over romans. They killed many of them, and they sent their heads to Baghdad, this cooled down the souls of people.
(al Bidaya wal Nihaya the year 362 h)
8. Shaykh al Islam Ibn taymiyyah revived Syria during the Mongol Invasion.
Ibn al Imad quoted ad-Dhahabi from his book Mu’jam al Shuyukh:
وأحيا به الشام، بل والإسلام، بعد أن كاد ينثلم خصوصا في كائنة التتار، وهو أكبر من أن ينبّه على سيرته مثلي، فلو حلّفت بين الرّكن والمقام لحلفت أني ما رأيت بعيني مثله، وأنه ما رأى مثل نفسه. انتهى كلام الذهبي.
“And he revived Syria, rather, Islam, after it was about to be torn apart, especially during the Mongol invasion. He is too great for me to describe his biography, for if I were to swear between the Corner (of the Kaaba) and the Station (of Ibrahim), I say: I have not seen anyone like him with my own eyes, and he has not seen anyone like himself.
Shadharaat adh-Dhahab fi Akhbar min Dhahab – Ibn al-‘Imad al-Hanbali 8/144