Can anyone quote a Hadith on minimum and maximum length of beard in Islam?
(SHIA point of view)
Allamah al Majlisi (in the book of Heliatul-Motaqin):
The Sunnah is keeping the beard in the normal (medial) size, not too short, not too long. It is Makruh to have beard more than a Qabzah(fist) and it has the probability of being Haram as well.
About the minimum size of it:
According to his explanations, it ought not to be too short that be similar to a person who cuts his beard completely.
About the maximum size of it: Imam Sadiq (a.s.) said:
The extra part of the beard(more than a fist) is in the fire.
أبي عبدالله (الامام صادق (ع)) قال : ما زاد من اللحية عن القبضة فهو في النار
So, in accordance with the mentioned quotation, and likewise in accordance with your photo, I reckon your beard size is okay and at least taller than its minimum .
It is not permissible for one to trim the hair along the jawbone unless it exceeds a fistful. Ulama have mentioned that it is wajib (obligatory) to grow the beard at least at fists’ length. The Ulama have deduced this from the following Hadith of the Prophet (SallAllahu Alayhi Wasallam) mentioned in Bukhari.....
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Beard growth varies - environment, genes and other factors play a role, for some people it just doesn't grow beyond a few patches.
So my friend, don't worry about its length but focus more on the spiritual aspect of religion and the life of Prophet Muhammad (PBUH)