Finally, stick to the advice your own heart gives you,
no one can be truer to you than that;
since a man’s soul often forewarns him better
than seven watchmen perched on a watchtower.

[καὶ βουλὴν καρδίας στῆσον,
οὐ γὰρ ἔστιν σοι πιστότερος αὐτῆς·
ψυχὴ γὰρ ἀνδρὸς ἀπαγγέλλειν ἐνίοτε εἴωθεν
ἢ ἑπτὰ σκοποὶ ἐπὶ μετεώρου καθήμενοι ἐπὶ σκοπῆς.]

The Bible (The Old Testament) (14th - 2nd C BC) Judeo-Christian sacred scripture [Tanakh, Hebrew Bible], incl. the Apocrypha (Deuterocanonicals)
Book 22b. Sirach (Ecclesiasticus) 37:13ff (Sir 37:13–14) [JB (1966)]
    (Source)

More on the history and acceptance of this Apocryphal book here and here.

(Source (Greek)). Other translations:

And let the counsel of thine own heart stand: for there is no man more faithful unto thee than it.  For a man's mind is sometime wont to tell him more than seven watchmen, that sit above in an high tower.
[KJV (1611)]

And establish within thyself a heart of good counsel: for there is no other thing of more worth to thee than it. The soul of a holy man discovereth sometimes true things, more than seven watchmen that sit in a high piece to watch.
[DRA (1899); 37:17-18]

Finally, stick to the advice your own heart gives you,
no one can be truer to you than that;
since a person's soul often gives a clearer warning
than seven watchmen perched on a watchtower.
[tr. NJB (1985)]

And trust your own judgment; no one's advice is more reliable. Sometimes your own intuition can tell you more than seven watchmen on a high tower.
[GNT (1976)]

Listen carefully to what
your own heart tells you,
since nothing is more faithful
to you than it.
At times a person’s intuition
keeps them informed
better than seven sentries
sitting high up on a lookout.
[tr. CEB (2011)]

And heed the counsel of your own heart,
for no one is more faithful to you than it is.
For our own mind sometimes keeps us better informed
than seven sentinels sitting high on a watchtower.
[NRSV (1989 ed.)]