Detainment Spell — ruling 1

Detainment Spell prevents mana abilities of the enchanted creature from being activated.

Detainment Spell — ruling 2

Morph isn't an activated ability, so Detainment Spell doesn't prevent face-down creatures from being able to turn face up.

Detainment Spell — ruling 3

Responding to a creature's activated ability being activated by moving Detainment Spell onto that creature won't affect the ability that was just activated.

Detainment Spell : règles, fonctionnement et interactions (MTG)

Detainment Spell is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Enchant creature Enchanted creature's activated abilities can't be activated. : Attach this Aura to target creature.

How it works : Detainment Spell

Original English text — Wizards of the Coast / Scryfall

#1September 25, 2006· Wizards of the Coast
Detainment Spell prevents mana abilities of the enchanted creature from being activated.
No other card is named in this ruling.
#2September 25, 2006· Wizards of the Coast
Morph isn't an activated ability, so Detainment Spell doesn't prevent face-down creatures from being able to turn face up.
No other card is named in this ruling.
#3September 25, 2006· Wizards of the Coast
Responding to a creature's activated ability being activated by moving Detainment Spell onto that creature won't affect the ability that was just activated.
No other card is named in this ruling.