Rashi on Leviticus 6:4/רש"י על ויקרא ו׳:ד׳

1‎ ופשט את בגדיו ‎ AND HE SHALL PUT OFF HIS GARMENTS — This is not compulsory (cf., however, Nachmanides) but it is a matter of decency so that he should not, through removing the ashes, soil the garments in which he has regularly to minister at the altar; in the clothes he wore when he boiled the pot for his master (a menial task) he should not pour out a glass of wine for him (an honourable office). On this account it states: And he shall put on other garments — inferior to those in which he ministers at the altar (Yoma 23b; Shabbat 114a).

2והוציא את הדשן AND HE SHALL BRING OUT THE ASHES that were heaped upon the ash-heap (not the ashes mentioned in v. 3). When it accumulated and there was no more room on the wood-pile (מערכה) he carried it out; this was not compulsory every day, whilst the תרומת הדשן (the taking out of the pan of ashes commanded in v. 3) was a daily duty (Yoma 20a).