"A man who cries out of fearing Allah, will not be put into the Fire until milk returns to the udder; and dust raised in the cause of Allah and the smoke of Jahannam will not be gathered together."

Sahih. Muhammad bin 'Abdur-Rahman is the Mawla of the family of Talbah, and he is from Al-Madinah, and trustworthy. Shu'bah and Sufyan Ath-Thawri reported from him.
Jami` at-Tirmidhi Book 36, Hadith 8
← Previous Hadith "When this Ayah was revealed: And warn your near kindred....(26:214), the Messenger of Allah (s.a.w) said: "O Safiyyah bint 'Abdul-Muttalib! O Fatimah bint Muhammed! O Banu 'Abdul-Muttalib! I have no authority on your behalf over Allah for anything. Ask me for whatever you want of my wealth."

Jami` at-Tirmidhi Book 36, Hadith 7 Next Hadith → "Indeed I see what you do not see, and I hear what you do not hear. The Heavens moan, and they have the right to moan. There is no spot, the size of four fingers in them, except that there is an angel placing his forehead in it, prostrating to Allah. By Allah! If you knew what I know, then you would laugh little and you would cry much. And you would not taste the pleasures of your women in the beds, and you would go out beseeching Allah. And I wish that I was but a felled tree."

This Hadith is Hasan Gharib. It has been related through routes other than this, that Abu Dharr said: "I wish that I was a felled tree." And it has been related from Abu Dharr in Mawquf form.

Jami` at-Tirmidhi Book 36, Hadith 9