Al-Ḥāfiẓ Ibn Rajab (d. 795 AH) said:

The scholars have differed [concerning what deeds the angels write]: Do they write everything that one says, or [is their writing relegated] to only reward or punishment?

These are the two most well-known opinions [in this matter].

The First Opinion: The Angels Write Everything One Says

ʿAlī ibn Abī Ṭalḥah narrated from Ibn ʿAbbās (may Allāh be pleased with both of them) who said: They [the angels] write everything that one says whether it be good or evil. To the extent that they even record his saying: “I ate,’’ “I drank,’’ “I went,’’ “I came”. On Thursdays, his actions are presented [to Allāh], his good and evil sayings are counted and his remaining [speech] is eliminated. For such is the saying of the Most High:

يَمْحُو اللَّهُ مَا يَشَاءُ وَيُثْبِتُ ۖ وَعِندَهُ أُمُّ الْكِتَابِ

‘Allāh erases what He wills (of His revelations and laws and of the deeds of His servants) and affirms what He wills and with Him is the Mother of the Book.’
[Al-Raʿd, 13:39]

The Second Opinion: The Angels Write Only Reward and Punishment

Narrated by Yaḥyá ibn Abī Kathīr who said: A man once mounted his donkey who [moved] causing him to trip. So he said: ‘What a wretched donkey!’ So the angel on the right said: ‘It [his saying] is not one of goodness, so I shall not record it.’ The angel on the left said: ‘It [his saying] is not evil, so I shall not record it.’ Allāh revealed unto the angel on the left to write everything that the angel on the right leaves off [recording]. Thus, [his saying]: ‘What a wretched donkey’ was recorded among his evil speech.’

The Opinion of Imām Ibn Rajab

Considering all of this, it would appear as if [speech] that is devoid of any goodness is considered evil except that one is not punished for it. For there exists sin that may remain unpunishable. [For example], it may be expiated due to refraining from engaging in major sin. However, the time used [to engage in such speech] has been lost on that which is effectively meaningless. This is a means by which regret and sorrow are felt on the Day of Judgement which is itself a form of punishment.

Source: Jāmīʿ al-ʿUlūm: 369
Translated by: Riyāḍ al-Kanadī