縱雲趕逐 The Pursuit on the Clouds
大仙與明月、清風縱起祥光，來趕三藏，頃刻間就有千里之遙。大仙在雲端裡向西觀看，不見唐僧。及轉頭向東看時，倒多趕了九百餘里。大仙与明月、清风纵起祥光，来赶三藏，顷刻间就有千里之遥。大仙在云端里向西观看，不见唐僧。及转头向东看时，倒多赶了九百余里。
逐句解 Line by line
The Great Immortal, with Bright Moon and Clear Wind, sprang up on auspicious light to overtake Sanzang, and in a moment had covered a thousand li.
縱起祥光, zòng qǐ xiáng guāng, "sprang up on auspicious light" — the coloured radiance an immortal travels on, one grade above an ordinary cloud. 頃刻間, qǐng kè jiān, in an instant. A 里, lǐ, is the Chinese mile, roughly half a kilometre; a thousand of them in a moment sets the scale of the chase.
From the cloud's edge the Great Immortal looked away west, but saw no sign of the Tang Monk.
He looks west, where a party fleeing west ought to be, and sees nothing. 向西觀看 takes 觀 as guān, "to look at" — the everyday reading, not the guàn that names the abbey he has just left.
And when he turned his head to look east, he had, on the contrary, overshot by nine hundred li and more.
Because he has already passed them. 倒多趕了 takes 倒 as dào, "on the contrary" — the word that turns the sentence into a joke. 九百餘里, nine hundred lǐ and more, overshot.
The pursuit is played as comic disproportion. The cloud is so fast that in a single instant it overleaps its quarry by nine hundred lǐ, and the terrible pursuer has to turn round and look back east for the monk he has left far behind.
The joke has a serious edge, though. A night of desperate riding, at the price of everyone's sleep, has bought the pilgrims a lead that a genuine immortal erases without noticing. There was never any prospect of outrunning him, and the reader now knows it a good few passages before the pilgrims do.