In one narration the wording is: "The people of 'La ilaha illallah' (There is no deity except Allah) will feel no loneliness at the time of death, nor in the grave." In the first narration there is a narrator, Yahya al-Himmani, and in the other a narrator, Mujashi' bin Amr, and both of them are da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأذكار / 16808