explanation of this hadith and Could you provide the exact translation and reference for this hadith "Everything has a polish, which takes away rust. The polish of the heart is dhikr."? and is it a sahih hadith?
This hadith has been quoted in sho'ab al-Imaan of imam al-Bayhaqi as a marfo' hadith on the authority of 'Abdullah ibn 'Omar and it is qualified as da'if by sheikh al-Albani in his a-Da'if al-Jami' (Hadith #1932), here the wording of the hadith in Arabic:
إِنَّ لِكُلِّ شَيْءٍ سِقَالَةً ، وَإِنَّ سِقَالَةَ الْقُلُوبِ ذِكْرُ اللَّهِ ، وَمَا مِنْ شَيْءٍ أَنْجَى مِنْ عَذَابِ اللَّهِ مِنْ ذِكْرِ اللَّهِ " ، قَالُوا : وَلا الْجِهَادُ فِي سَبِيلِ اللَّهِ ؟ قَالَ : " وَلَوْ أَنْ تَضْرِبَ بِسَيْفِكَ حَتَّى يَنْقَطِعَ "
"For everything there is a polish, and the polish for the hearts is the dhikr (remembrance) of Allah. There is nothing more potent in saving a person from the punishment of Allah than the dhikr of Allah." It was said: Not even Jihaad in the path of Allah. So he replied: "Not even if you were to continue striking with your sword until it breaks." (Source of the translation see here)
al-Manawi in his fath al-Qadir commentary on al-Jami' as-Saghir of as-Suyuti added an explanation on the qualification saying:
In the following I will translate from Arabic, this is my own translation take it carefully
فيه سعيد بن حسان وهما اثنان أحدهما قال أحمد غير قوى والآخر قال الذهبى متهم بالوضع (Source Hadith #8155)
In the narrator chain there's Sai'd ibn Hassan and they are two (people) one of them was considered as not strong (rather weak) by imam Ahmad and the second was accused for fabrication by a-Dhahabi.