Shaykh Ibn ‘Uthaymeen said: 

Undoubtedly it is better to adhere to the dhikrs narrated (in the texts). When a person rises from bowing, he should say, “Rabbana wa laka’l-hamd” and not add the word “wa’l-shukr”, because this was not narrated in the texts. 

There are four narrated versions of what is to be said after rising from bowing: 

1 – Rabbana wa laka’l-hamd (Our Lord, and to You be praise) 

2 – Rabbana laka’l-hamd (Our Lord, to You be praise) 

3 – Allaahumma Rabbana laka’l-hamd (O Allaah, Our Lord, to You be praise) 

4 – Allaahumma Rabbana wa laka’l-hamd (O Allaah, Our Lord, and to You be praise) 

These four versions may all be said, but not all at once, rather you should say one of them one time and another another time. So in some prayers you could say, Rabbana wa laka’l-hamd (Our Lord, and to You be praise); and in some prayers you could say, Rabbana laka’l-hamd (Our Lord, to You be praise); and in others say, Allaahumma Rabbana laka’l-hamd (O Allaah, Our Lord, to You be praise); and in yet others say, Allaahumma Rabbana wa laka’l-hamd (O Allaah, Our Lord, and to You be praise). 

With regard to the words wa’l-shukr, this was not narrated so it is better not to say it.