To what extent is the narration from Tawus regarding the desirability of offering food on behalf of the deceased authentic, and can it be used as evidence that the dead are tried in their graves for seven days?

The chain of transmission for Sufyan al-Thawri's narration from Tawus in "Al-Zuhd" is weak due to discontinuity between them; it is a mursal narration and thus holds no evidentiary weight. The jurisprudence of this narration is explained by Ibn Hajar in the chapter "Preparing Food for the Deceased's Family," which is permissible as in the hadith (definition), "Prepare food for Ja'far's family." The narration recommends providing food as charity for the deceased, without gathering at the deceased's home, and this is considered one of the greatest acts of righteousness and has immense reward. Al-Suyuti and some scholars have concluded that the deceased is tested in their grave for seven days, based on this and other narrations, while others believe the testing occurs only once, or they differentiate between the believer and the hypocrite.