جامع الترمذي

Narrated Sahl bin Abi Umamah bin Sahl bin Hunaif:

From his father, from his grandfather, that the Prophet (ﷺ) said: "Whoever asks Allah for Martyrdom sincerely in his heart, Allah will grant the status of martyrdom for him, even if he were to die in his bed."

[Abu 'Eisa said:] This Hadith is Hasan Gharib as a narration of Sahl bin Hunaif. We do not know of it except from the report of 'Abdur-Rahman bin Shuraih. 'Abdullah bin Salih reported it from 'Abdur-Rahman bin Shuraih, and 'Abdur-Rahman bin Shuraih's kunyah is Abu Shuriah, and he is from Iskandarani.

There is something on this topic from Mu'adh bin Jabal.