Finishing a good deed is not the same as knowing it was accepted. Ibrahim (AS) and Ismail (AS) asked for acceptance while building the Ka'bah itself. These prayers keep sincerity alive after the work is done.
Rabbana taqabbal minna, innaka anta-s-Sami'u-l-'Alim.
“Our Lord, accept this from us. Indeed, You are the Hearing, the Knowing.”
The prayer Ibrahim (AS) and Ismail (AS) made while raising the foundations of the Ka'bah. Even during a great act of worship, they asked Allah (SWT) to accept it.
Rabbana atina fi-d-dunya hasanah, wa fi-l-akhirati hasanah, wa qina 'adhaba-n-nar.
“Our Lord, give us in this world good and in the Hereafter good, and protect us from the punishment of the Fire.”
A short, complete prayer asking Allah (SWT) for every kind of genuine good in this life, lasting good in the Hereafter, and protection from the Fire.
Rabbana atmim lana nurana wa-ghfir lana, innaka 'ala kulli shay'in qadir.
“Our Lord, perfect for us our light and forgive us. Indeed, You are over all things competent.”
A prayer for complete light and forgiveness on the Day believers will need both. It asks Allah (SWT) to carry faith to its good completion, not merely to give a promising beginning.