The Impurity, Filth
وَ قَالُوا ع فِي الْأَرْضِ تُصِيبُهَا النَّجَاسَةُ لَا يُصَلَّى عَلَيْهَا إِلَّا أَنْ تُجَفِّفَهَا الشَّمْسُ وَ تَذْهَبَ بِرِيحِهَا فَإِنَّهَا إِذَا صَارَتْ كَذَلِكَ وَ لَمْ يُوجَدْ فِيهَا عَيْنُ النَّجَاسَةِ وَ لَا رِيحُهَا طَهُرَتْ
And Imam-asws said regarding the ground hit by ‘النَّجَاسَةُ’ the impurity: ‘Do not pray Salat upon it except if the sun has dried it and its smell has gone. When it becomes like that and an eye of the impurity is not found in it nor its smell, it has been purified’.[1]
[1] Bihar Al-Anwaar V 77 – The Book Cleanliness – Ch 12 H 17 (Chapters on uncleanness and its purifiers)