Musannaf Ibn Abi Shayba 6:855

Shababa ibn Sawwar narrated to us, from Layth ibn Sa'd, from Ibn Shihab, from 'Abd al-Rahman ibn Ka'b ibn Malik, from Jabir ibn 'Abd Allah, that he informed him that the Prophet (peace be upon him) used to combine two men from the martyrs of Uhud in one grave. He would say, "Which of them was more learned in the Quran?" When one of them was pointed out to him, he would place him forward, meaning in the *lahd* (niche).