Green’s Dictionary of Slang

1. a racing tipster.

1843		Ainsworth’s Mag. III 220: What’s to win the Derby? [...] What say the prophets?
1852		Greenock Advertiser 1 June 4/1: Back Ben, and he’s sure to lead you on to Victory. Remember, there is but one horse, and benjamin is his Prophet!
1862		Times 31 Dec. n.p.: Prophets, tipsters and welshers – the parasites of the ring.
1872		Bicester Herald 21 June 5/5: The best Tip for a Sporting Prophet — the toe of your boot. Let him have it!
1884		Pall Mall Gazette 3 May 1/2: The skilful arguments of the ‘prophet’ of a daily or weekly newspaper .
1891		Bird o’ Freedom (Sydney) 7 Feb. 4/1: Any prophet getting home with three winners in succession [...] will find that he is not without honor in our country.
1894		Waterford Mirror 16 Aug. 5/3: The old prophet elected the horse.
1904		Sydney Sportsman (Surry Hills, NSW) 20 July 3/4: Asked ‘The Trier’ [...] why he didn’t ‘break’ a ‘blowfly’ that is always pestering him and forcing his undesirable company on him. ‘Oh,’ quoth the turf prophet [etc].

2. (N.Z. prison) a highly knowledgable veteran inmate.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 146/2: prophet n. an experienced inmate well­ versed in prison culture, with a wide­ ranging knowledge of the criminal justice system.