In Ibn Kathir's Tafsir (specifically his chapter on the last ayaat of Surah al-Imraan), he mentions the following story:
Al-Hafiz ibn `Asakir mentioned in the biography of `Abdullah bin al-Mubarak, that Muhammad bin Ibrahim bin Abi Sakinah said,
“While in the area of Tarsus, `Abdullah bin al-Mubarak dictated this poem to me when I was greeting him goodbye. He sent the poem with me to al-Fudhayl bin`Iyad in the year 170:
O Worshipper of the Two Holy Masjids!
Had you witnessed us in the battlefield
You would have known that, compared to our Jihad,
Your worship is child's play.
For every tear you have shed upon your cheek,
We have shed in its place, blood upon our chests.
You are playing with your worship,
While worshippers offer your worship
Mujahideen offer their blood and person (life).
The smell of nice perfume of is for you,
And our perfume is the dust and dirt (which is more pure),
And it has reached us from the sayings of our Prophet,
The martyr is not dead,
This is a true correct saying, in which there is no lie.
The dust of the people of Allah is never equal,
To a thousand men, whilst the smoke is climbing.
This is the book of Allah between us,
The martyr is not dead – and this is no lie.
“I met al-Fudayl ibn `Iyad in the Sacred masjid and gave him the leter. When he read it, his eyes became tearful and he said, 'Abu `Abdur-Rahman (`Abdullah bin al-Mubarak) has said the truth and offered sincere advice to me.' He then asked me, 'Do you write the Hadeeth?' I said, 'Yes.' He said, 'Write this Hadeeth as reward for delivering the letter of Abu `Abdur-Rahman to me.' He then dictated,