Abū Naʿaym al-Aṣbahānī (d. 430 AH) said:

Muʿādh, Abū ʿUbaydah, Shuraḥbīl ibn Ḥasanah, and Abū Mālik al-Ashʿarī (رضي الله عنهم) were all stabbed in the same day [during battle]. Muʿādh said: “It represents but the mercy of your Lord–the Exalted in Might—and the invocation of your Prophet (صلى الله عليه وسلم), and a means by which the souls of the righteous are taken. O Allāh! Give the family of Muʿādh the greatest allotment of this mercy.” The afternoon did not reach him except that his first-born son, ʿAbd al-Raḥmān, was also stabbed, from whom he derived his kunyah—the most beloved person to him. When Muʿādh returned to the masjid, he found his son in a state of grief. He said: “O ʿAbd al-Raḥmān! How are you doing?” He replied: “O dearest father:

الْحَقُّ مِن رَّبِّكَ فَلَا تَكُن مِّنَ الْمُمْتَرِينَ

“(This is) the truth from your Lord, so be not of those who doubt.”
(Āli ʿImrān, 3:60)

Muʿādh replied: “As for myself:

سَتَجِدُنِي إِن شَاءَ اللَّهُ مِنَ الصَّابِرِينَ

“In shāʾ Allāh (if Allāh wills), you shall find me of al-Ṣābirīn (the patient ones).”
(al-Ṣāffāt, 37:102)

He died that night and was buried the following day.

Imām Abū al-Farj ibn al-Jawzī (d. 597 AH) said:

ʿAmr ibn Qays narrated from those around Muʿādh that, upon his death, he said: “Greetings to my demise, a visitor in intervals, beloved he approaches in destitution. O Allāh! I have always feared You and on this day I put my hopes in You. O Allāh! Indeed, you assuredly know that I do not love this worldly life nor do I desire a prolonged stay in it for its flowing rivers or to plant trees. Rather, for the thirst of midday [when fasting], and bearing the hours of affliction [in the night prayer] and riding to the gatherings of remembrance in order to crowd around the scholars.”

Narrated by al-Ḥārith ibn ʿUmayrah al-Zubaydī who said: Indeed, I sat with Muʿādh ibn Jabal (رضي الله عنه) while he died. He began to faint and regain consciousness continually. Upon waking, I heard him say: Strangle the life from me as you strangle. By Your Might! Indeed, You know that I love You.”

Source: Ḥilyah al-Awliyāʾ 1:240 and Al-Thabāt: 118-119
Translated by: Riyāḍ al-Kanadī