Strange, is it not? that of the myriads who
Before us pass’d the door of Darkness through
Not one returns to tell us of the Road,
Which to discover we must travel too.

Omar Khayyám (1048-1123) Persian poet, mathematician, philosopher, astronomer [عمر خیام]

Rubáiyát [رباعیات] [tr. FitzGerald, 2nd ed. (1868), # 67]
    (Source)

The same translation is used in the 3rd ed. (1872), # 64; 4th ed. (1879), # 64; 5th ed. (1889), # 64.

Alternate translations:

These travelers have departed, and of them all, not one has returned to tell us of the hidden things concealed behind the veil. Oh, devout man, it is by a humble heart, and not by prayer, that the things which concern thy soul will be brought to a favourable issue, for prayer is of no avail to a man without sincerity and contrition.
[tr. McCarthy (1879), # 81]

Of all who have set out upon the long journey, who has come back, that I may ask him tidings? My friends, take heed to let naught go by in the hope of hopes for, be sure, you will not come back again.
[tr. McCarthy (1879), # 160]

Full many a hill and vale I journeyed o'er;
Journeyed through the world's wide quarters four,
But never heard of pilgrim who returned;
When once they go, they go to come no more.
[tr. Whinfield (1883), # 129]

Who e'er returned of all that went before,
To tell of that long road they travel o'er?
Leave naught undone of what you have to do,
For when you go, you will return no more.
[tr. Whinfield (1883), # 144/258]

They go away, and none is seen returning,
To teach that other world's recondite learning;
'T will not be shown for dull mechanic prayers,
Gor prayer is naught without true heartfelt yearning.
[tr. Whinfield (1883), # 148/266]

Of Those who have the "Long Road" travelled o'er,
Not One will bring Thee News of it, before
Thou too shalt go, and heed Thee that Thou leavest
Without Regret, Thou shalt return no more.
[tr. Garner (1887), 2.7]

Alas, that joy takes flight: not many hearts
The pangs of desolating grief are spared;
No traveller from Death's dark realm returns
To tell us how his fellow-pilgrims fared.
[tr. Bowen (1976), # 56]

Much have I wandered about far and wide,
I have wandered as far as every horizon/;
I have heard of nobody who came from this road,
The road he went by, the road of no return.
[tr. Avery/Heath-Stubbs (1979), # 49]