Sayyiduna Anas bin Malik (may Allah be pleased with him) says: It is the Sunnah that the burial of the deceased and the throwing of soil should begin from the side of the qiblah.
Imam Tabarani recorded it in al-Mu'jam al-Awsat. Its chain contains a narrator, Ubaydah bin Hassan, and he is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الجنائز / 4236