(3) When a man vows a vow unto the LORD, or swears an oath to bind his soul with a bond, he shall not break his word; he shall do according to all that proceeds out of his mouth.
(29) In those days they shall say no more: ‘The fathers have eaten sour grapes, And the children’s teeth are set on edge.’ (30) But every one shall die for his own iniquity; every man that eats the sour grapes, his teeth shall be set on edge.
(יב) רבי אלעזר בן שמוע אומר, יהי כבוד תלמידך חביב עליך כשלך, וכבוד חברך כמורא רבך , ומורא רבך כמורא שמים.
(12) Rabbi Elazar ben Shamua says: Let the honor of your student be dear to you as your own, and the honor of your fellow like the reverence of your teacher, and the reverence of your teacher like the reverence of Heaven.
(9) Even one that is slack in his work is brother to him that is a destroyer. .
כדרך שמוזהר בעה"ב שלא יגזול שכר עני ולא יעכבנו כך העני מוזהר שלא יגזול מלאכת בעה"ב ויבטל מעט בכאן ומעט בכאן ומוציא כל היום במרמה אלא חייב לדקדק על עצמו בזמן שהרי הקפידו על ברכה רביעית של ברכת המזון שלא יברך אותה, וכן חייב לעבוד בכל כחו שהרי יעקב הצדיק אמר כי בכל כחי עבדתי את אביכן, לפיכך נטל שכר זאת אף בעולם הזה שנאמר ויפרץ האיש מאד מאד. /סליקו להו הלכות שכירות/.
Rambam, Mishneh Torah, Laws of Hire 13:7
Just as the employer is commanded not to deprive the employee of his wages or withhold them, so too is the employee commanded not to steal from his employer by slacking off a bit here and there and thus dishonestly spending his workday. It is incumbent on him to carefully utilize all of his time...and he is obligated to work with all of his might, as the righteous Patriarch Yaakov declared to his wives: "With all my might I worked for your father."