“You can.”

Variant Do all the good you can, in all the ways you can, to all the souls you can, in every place you can, at all the times you can, with all the zeal you can, as long as ever you can.
In the sermon titled "The Use of Money" Wesley said, "Employ whatever God has entrusted you with in doing good, all possible good, in every possible kind and degree . . . to all men." This sermon is in the collection titled "Wesley's Standard Sermons." They are called "standard" because all Methodist preachers were instructed to read them and use them in interpreting the Christian faith.
Disputed
Variant: Do all the good you can. By all the means you can. In all the ways you can. In all the places you can. At all the times you can. To all the people you can. As long as ever you can.
Source: According to Richard Heitzenrater, Professor of Church History and Wesleyan Studies at Duke Divinity School, there is no evidence that John Wesley ever wrote the rule that is attributed to him.

quoted by Book of African-American Quotations (Page 47).

Source: Created for Greater Things

Source: Love Is Letting Go of Fear

Tom Fitzgerald, a Disney Imagineer, as quoted in Ask Dave by Dave Smith (27 February - 12 March 2013) https://d23.com/d23-presents-ask-dave-answers-to-questions-asked/:
:: Despite its frequent publication, that is not a Walt Disney quote. We checked with Imagineer Tom Fitzgerald for the definitive answer: "I am very familiar with that line because I wrote it! It was written specifically for the Horizons attraction at Epcot and used in numerous ways, from dialogue in the ride to graphics. I find it amusing that the Science of Imagineering DVD series attributes it to Walt Disney, but I guess I should be flattered."
::* Disney Trivia from the Vault (2012) by Dave Smith, p. 243
Misattributed
Variant: If you can dream it, you can do it.

Original Icelandic quote: Þið getið farið heim. Þið getið farið úr Evrópu. Þið getið farið bara hvert sem þið viljið.
A reference to Brexit following Iceland's 2-1 win against England in the last-16 of the 2016 UEFA European Football Championship on 27 June 2016.
Source: [Eiríkur Stefán Ásgeirsson, Verð að vera ég sjálfur, https://timarit.is/page/6731435, 4 July 2020, Fréttablaðið, 2 July 2016, 22, Icelandic]
Source: [Ed Aarons, ‘You can go out of Europe’: Iceland commentator savours win over England, https://www.theguardian.com/football/2016/jun/27/you-can-go-out-of-europe-iceland-commentator-england-euro-2016, 4 July 2020, The Guardian, 27 June 2016]
Source: [England Has Left Europe Twice in a Week and That Icelandic Commentator Is Ecstatic, https://time.com/4384954/iceland-england-euro-2016-brexit-soccer-football/, 4 July 2020, Time, 27 June 2016]
Source: [Mark Critchley, England vs Iceland: Icelandic commentator goes wild again after historic Euro 2016 win, https://www.independent.co.uk/sport/football/international/england-vs-iceland-icelandic-commentator-goes-wild-again-after-brilliant-win-a7106841.html, 4 July 2020, The Independent, 28 June 2016]