Me and my group wondered what counts as a "small portion of the creature’s body". Do blood or hair count?
In the resurrection spell description, it is written:
small portion of the creature’s body still exists
The remains of a creature hit by a disintegrate spell count as a small portion of its body.
In the FAQ I found only this:
If you cast resurrection on dragonhide armor does the dragon come back to life?
Yes. The resurrection spell states that “so long as some small portion of the creature’s body still exists, it can be resurrected” and that “the condition of the remains is not a factor.” It would be up to the DM to determine the age and kind of the dragon resulting from such a spell, using the guidelines for minimum size required to make the armor in question (see page 284 in the DMG). The same would apply to any object crafted from part of a living creature, such as leather or hide armor, a necklace of boar tusks, or a cloak made from the fur of a dire weasel.