He is swift in his pursuit إنه لحثيث التوالي

It is said, he is quick in his pursuit; this is said of a horse, and its pursuit is its hindquarters, its legs and tail, and the pursuit of everything is its end.
It is used to describe a diligent and swift man.

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 This meaning is reflected in English proverbs and expressions such as:

Quick off the mark.

Or:

Fast and furious.

And for the closest meaning in terms of seriousness and speed:

Swift as the wind.

Thus, the Arabic proverb describes a very serious man, quick in action and accomplishment, just as it describes a swift horse.

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ويقال، لسريع التوالي؛ يقال ذلك للفرس، وتواليه: مآخيره، رجلاه وذنبه، وتوالي كل شيء، أواخره.
يضرب للرجل الجاد المسرع.