The Messenger of Allaah (sallal-laahu-alayhi-wasallam) said:

‘Indeed Allaah is Pure and He does not accept, except that which is pure’

Shaikh Saaleh Al Fawzaan (may Allaah preserve him) commented on this hadith saying:

In this hadith he (sallal-laahu-alayhi-wasallam) described Allaah (The Exalted] that Allaah (Glorified Be He and Free Is He from all imperfections, faults and weaknesses) is Pure.  Allaah is pure, meaning: Allah is free from all imperfections and deficiencies.  He is Pure in His Essence, in His Names and Attributes, and in His Commandments and Prohibitions.  Allaah is Pure in every aspect and imperfection cannot reach Him. And for that reason Allaah does not accept actions, statements and intentions except that which is pure.  He does not accept filthy statements, actions and intentions. Allaah does not accept except the pure, as Allaah (The Most High) said:

إِلَيْهِ يَصْعَدُ الْكَلِمُ الطَّيِّبُ وَالْعَمَلُ الصَّالِحُ يَرْفَعُهُ

‘To Him ascend (all) the goodly words'[35:10]

Allaah does not accept, except good speech and good actions. As for filthy speech, then indeed Allaah rejects and hates it, such as lies, backbiting, tale carrying, abuse, false speech and false testimony, and all filthy statements, (such as) shirk and kufr.  All of this is filthy speech and does not ascend to Allaah, and they are not accepted.

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[Source:’Al Minhatu Ar-Rabbaaniyyah Fee Sharh Arba-een Nawawiyyah’ page:133-134; slightly paraphrased and abridged]