Of the etiquettes of du’a is that a person be in a state of wudu (ritual purity).
This is confirmed in the hadith of Abu Musa al-Ash’ari in which he stated that the Prophet, peace and blessings of Allah be upon him, after the Battle of Hunayn, called for water, performed wudu, then raised his hands and said:
“O Allah! Forgive ‘Ubayd ibn ‘Amir!”
Abu Musa said, “I could see the whiteness of his armpits.” (Recorded in al-Bukhari)