Shimon ben Shetach was in the hard labor flax trade.

His students said to him: “Rabbi, remove [this work] from yourself,

and we will buy you a donkey and you won’t have to work so hard.”

They went and bought a donkey for him from a Saracen.

When they returned they found a pearl on it .

They came to him and told him:
“From now on you won’t have to work any more!”

He replied:“Why not?
– “We bought you a donkey from a Saracen
and  then found  on it a pearl.”

Shimon asked: “And did its master know?”

They replied: “No.”

He said: “then go and return it.”

Why they  questioned ?:
Did not… Rav [Abba Arikha]: “They said before Rabbi [Yehuda the Prince],
all agree that it is permitted [to retain] that which a none jew  lost.’”? [if
Accordingly, why did Shimon ben Shetach return the pearl?]

He replied:
"What do you think,
that Shimon ben Shetach is a barbarian?!

More than Shimon ben Shetach wanted  money ,
he wanted to hear [the non-Jew] say
‘Blessed be the God of the Jews.’

Talmud Yerushalmi, Bava Metzia 2:5