GEN1350 A wageworker must be careful not to steal time from his employer … if for his own personal needs, a day laborer interrupts the work he is hired to do – he is a thief.  … Furthermore, even if one performs a mitzvah during his working hours, it will not be ascribed to him as an act of righteousness but rather, as a transgression.   For a transgression can never be a mitzvah.  This is explicitly stated in Scripture Isaiah 61:8: “I loathe burnt offering that are [derived from] stolen [money].”   Similarly, they of blessed memory have said Baba Kama 94a: “If a person has stolen a se’ah [a measure] of wheat, ground it, baked it, and recited the blessing over it [when separating challah], this is blasphemy but not a blessing, as it states Psalms 10:3: “The thief who blesses has blasphemed the Eternal.”   PATH 58-9