The later Quartos, including those of 1676, 1683, 1695, and 1703, spelling apart, have the same reading.
In the first Folio, followed substantially by the rest, we find only these words:
'And what's vntimely done. Oh come away,
My soule &c.'
Rowe, Pope, Hanmer and Warburton followed the Folios.
Theobald first adopted the text of the Quartos. In his Shakespeare Restored, p. 108, he had suggested 'Happily, slander,' or 'Happily, rumour;' in his edition he supplied the blank thus:
'And what's untimely done. For, haply, Slander
(Whose whisper &c.'
Hanmer, in his copy of Theobald's edition, erased the passage with a pen.
Johnson, and Steevens in his editions of 1773, 1778 and 1785, followed Theobald.
Capell filled the hiatus by 'So, haply, slander,' and was followed by Steevens (1793) and most modern editors. Mason seems not to have consulted Capell's edition, for in 1788 he puts forward this reading as a conjecture of his own.