The People of Sabt
Prophet Musa (A) had taught the Bani Israa'il (Jews) to designate one particular day for the worship of Allah . On that day they were to abandon all their business or leisure activities. Originally, the day of Friday was specified, but at the request of the Bani Israa'il, it was changed to Saturday. This day, the Sabbath, became a holiday for the Jews and on Saturdays Prophet Musa (A) used to address a special congregation and preach to the people. For many years after Prophet Musa (A), the Sabbath was faithfully observed as a religious day. However, in the time of Prophet Dawood (A), one group of the Bani Israa'il, who lived at the seaport of Ela, broke the Divine rule. The people of Ela were mainly fishermen and fished the seas everyday except Saturday. Allah tested their faith by making the fish become very easy to catch on Saturdays.

The Holy Qur'an says:
And (O Muhammad) ask them about the (people of the) town which was beside the sea; when they exceeded (the limits) in the Sabbath when their fish came to them on the day of their Sabbath, appearing on the surface of the water; and on the day they did not observe the Sabbath, they (the fish) did not come unto them. Thus did We try them, for they were transgressing. And when a part of them said, "Why do you preach to those whom Allah would destroy or punish by a severe torment?" They replied, "To be free from blame before your Lord, so that perhaps they may become pious."  (Quran 7:163-164)
The fishermen were tempted by the easy catches to be made on Saturday and they thought of a plan to get around the Divine restriction. They decided to dig trenches and canals to divert the fish. On Saturdays, the canals were opened and the fish would swim into them in large numbers. At night, before the fish could return back to the sea, the canals were dammed. Then on Sundays the fishermen would easily catch all the trapped fish.

The wise and pious people of the tribe advised these greedy fishermen not to violate the command of Allah . They considered it their duty to guide those who were in error, because otherwise they would also be to blame for the consequences. However, the fishermen continued disobeying the Divine commandment and even boasted about their cleverness.

Finally, the punishment of Allah came down and their faces were transformed into those of animals. After three days and nights all the sinners were destroyed. The Holy Qur'an says:
And indeed you know of those amongst you who transgressed on the Sabbath, so We said unto them, "Become apes, despised and spurned!" And We made it a lesson for (those of) their own times and those (of their posterity) who came after them and a guidance for those who guard against evil.  (Quran 2:65-66)