Combining two Actions
Repeating this Dua:
﴿ رب اغفر لي و لوالديّ ﴾
‘O Allaah forgive me & my parents’
combines between two actions of worship: being good to parents & seeking forgiveness.

From Ibn Shihab who said that Anas bin Malik informed him that
the Messenger of Allaah sallAllaahu alayhi wa sallam said:
” مَنْ أَحَبَّ أَنْ يُبْسَطَ لَهُ فِي رِزْقِهِ، وَيُنْسَأَ لَهُ فِي أَثَرِهِ ،
فَلْيَصِلْ رَحِمَهُ “.
‘Whoever would like that his provisions are increased many-fold and that
he has a long blessed life then he should keep good relations with his
relatives.’
[Collected by Bukhari and Muslim]