Берешит 31:6 Галаха: Mishneh Torah, Hiring & Kitzur Shulchan Arukh

.....Just as the employer is cautioned to not steal wages from the poor and not to withhold them, so too are the poor cautioned to not "steal" from the work of his employer by being idle a little here and a little there until he has spent the whole day in deception. Rather, he is obligated to be punctilious with himself regarding time. After all (the sages) were punctilious in the matter of the fourth blessing of the grace after meals, that the employee should not recite it (so as not to take him away from his work), so too the employee is obligated to work with all his strength. Behold, Jacob the righteous said "with all my strength I worked with your father" (Genesis 31:6) he therefore received reward for it, even in this world, as it is stated "and the man profited very much" (Genesis 30:43)

Just as the employer is admonished not to rob the worker of his wages, and not to delay payment, so is the worker admonished not to cheat his employer by wasting time at work. He must work with all his strength [ability,] as our father, Jacob, peace unto him, said, "That I served your father with all my strength."⁷Genesis 31:6. Therefore, a worker is not permitted to work all night, and hire himself out during the day because he has been weakened by the night work. Similarly, it is not permitted to work your animal at night and hire it out for work during the day. A worker is not permitted to starve or afflict himself, for this weakens his physical strength, and he will not be able to do the work for his employer properly. This law applies also to a teacher. (see Chapter 165:12)