Walaikumus Salam
The floor will be considered pure unless you've seen some impurity and you are certain that it is impure. There is a maxim in jurisprudence:
اليقين لا يزول بالشك
"Certainty is not dispelled by doubt."
Also a similar question was asked in this thread to which Mufti Abuhajira answered:
Allah ta'ala knows best.