Ibn al-Jawzī said,
"Know that repeating the intention for prayer is caused by stupidity and ignorance. If a scholar were to enter (a room) and a person stands up for him (out of respect) and says: 'I intend to stand up out of respect for this scholar...

...who has entered this gathering' then people who declare him an idiot. (The action of) standing up made his intention clear. Standing up for prayer is only done for one reason, and it does not take long. This is utter ignorance."

[The Devil's Deception (Talbīs Iblīs), Translated & Published by Dār As-Sunnah]