Sayyiduna Abu Umamah (may Allah be pleased with him) said: When Sayyidah Umm Kulthum (may Allah be pleased with her), the daughter of the Messenger of Allah (peace and blessings be upon him), was placed in her grave, he (peace and blessings be upon him) recited: "From it (the earth) We created you, into it We shall return you, and from it We shall bring you out once again" [Surah Ta Ha: 55], and said: 'Bismillah, wa fi sabilillah, wa 'ala millati Rasulillah' (In the name of Allah, in the path of Allah, and upon the religion of the Messenger of Allah). When her niche (lahd) was built over her, he (peace and blessings be upon him) began throwing pieces of palm stalk to them, saying: "Fill the gaps between the bricks." Then he (peace and blessings be upon him) said: "This is really nothing, but the hearts of the living are comforted by it."
This chain is weak.
It is also narrated, from Makhul from the Prophet (peace and blessings be upon him) in mursal form, that he (peace and blessings be upon him) said: "Close the gap with clay," and his (peace and blessings be upon him) saying: "It neither benefits nor harms, but it cools the eyes of the living."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6726