Someone said :
I can't believe I'm about to post this, but here goes:
Clean your hands, use a sterile latex glove, and dab a bit of water-based lubricant on the glove’s fingertips. Then gently insert your fingers into his anus. Carefully push them inwards and upwards, against the rectal lining towards his front side. Move your fingers roughly the direction of his navel.
You do not have to push in too far, just a little more than an inch--about 3 cm. Then you will touch the prostate gland, a small round bulb of tissue about the size of a large walnut. Give it a gentle massage by rubbing it lightly along its sides. Do not press hard on the gland’s central portion, as that is where some sensitive nerves are located. Do not touch the prostate gland with your fingernails.
At some point, your partner may feel like he wants to urinate, even though he does not have to. That may feel somewhat confusing, but try to reassure him and, if he is okay with it, you can continue.
Your partner will become stimulated and may even ejaculate - but it is all right if ejaculation does not occur, as it doesn’t always happen.
And that, children, is how you give your partner a prostate massage.