How did Hashirama know about Tsunade's strength ?

[Ridoku X]

In the latest chapter we saw Hashirama commenting on Sakura's power up.
He said that it might be "worse" than Tsunade's.
So my question is...How the hell did Hashirama know of Tsunade's power ?? he had only seen her as a kid if I am not mistaken !

 

[Horus]

Because she was probably very very destructive at a young age, being senju and all, and her temper is not nice.

 

[Zuru]

Well, he must have just implied it, she is HIS granddaughter after all. =D

 

[S A G E]

It implies that current Sakura is of the same level as 5 year old Tsunade.

 

[minatoisagod]

maybe tsunade was at this level when he was alive hell she had that seal from birth it seems

 

[Prime Rib]

tsundae has raw str even as a kid she was most likely very strong