Kommentar zu Schemuel II 3:26

From Bor HaSiroh. The name of a place [But] the Rabbis said: A well and a thorn caused Avner to be killed, by not grasping unto the deeds of Dovid, by [ignoring] the jug of water that [Dovid] took from [under] the head of Shaul¹⁴This is reference to Shmuel I, 26,12 where Dovid was being pursued by Shaul and Avner. Dovid found them sleeping and hence vulnerable. Not wanting to harm them but wanting to show Shaul he had been there, Dovid took the spear and the jug of water that was underneath Shaul’s head. and also [by ignoring] the corner of Shaul's garment¹⁵This is a reference to Shmuel I, 24,5 where Shaul, in pursuit of Dovid, stopped temporarily inside the cave where Dovid was hiding with his men. Dovid did not kill him but surreptitiously caught off the corner of Shaul’s garment. [Avner dismissed this and] he said "Perhaps one of the thorns caught upon [the garment] and tore it.