Fingerprints

The answer – and Allah is the One who grants success – is that if it is established that every human being has a fingerprint specific to him, then it is permissible to act upon it; rather, it is obligatory upon the judge to act upon the fingerprint in other than ḥudūd (prescribed penalties) – that is, in financial matters and rights. The proof for that is:
1. That what is required of the judge is that he rule with the truth; so when the truth becomes clear to the judge, it becomes obligatory upon him to give effect to it and to rule accordingly.
2. That the fingerprint is in the position of the signet-ring with which letters and messages are sealed. The Messenger of Allah (May Allah bless him and his family and grant them peace) used to have a ring with which he sealed his letters and messages, and it is narrated that he forbade people from taking a ring like his. After him, the caliphs likewise had rings with which they sealed their letters and messages.
3. That the bayyinah (proof) by which it becomes obligatory upon the judge to rule is broader than (oral) testimony; its reality is: that by which the truth of the claim becomes clear to the judge.
They [the scholars] have said: “Droppings indicate the camel; footprints indicate the journeying; will the heaven with its constellations and the earth with its pathways not indicate the All-Subtle, the All-Aware?” – and the fingerprint falls under this heading, and its indication is decisively inferential.
Yes, and we only said that one acts upon the fingerprint in other than ḥudūd because the duty in ḥudūd is to avert them as far as possible. The Prophet (May Allah bless him and his family and grant them peace) said: “Repel the ḥudūd as much as you find a way ,” and he said: “Ward off the ḥudūd by doubts.” And from ʿAlī (Peace be upon Him): “That I err in pardoning is more beloved to me than that I err in punishing.” And it is narrated from the Prophet (May Allah bless him and his family and grant them peace) that he used to suggest to the thief what would make the ḥadd fall away from him.
On that basis, if it is established by way of fingerprints that a man is the one who took the property from its secure place, then the man is bound to guarantee (compensate) the property, and the ḥadd is averted from him.
This, and it is necessary that it be established with the judge that fingerprints do not resemble one another.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2