Source:dota2.gamepedia.com/Bash

Bash

Bash is a passive ability that gives a unit a chance to deal bonus damage and stun its target on attack. Multiple sources of Bash will stack, with the longest-duration stun overshadowing the others, but heroes with Bash abilities are generally prevented from purchasing Skull Basher and Abyssal Blade. Illusions cannot Bash, but the stun animation will still play over the affected hero.
nbsp;
A bash has two components: the damage and the stun. Both are governed by the rules of damage types in their interaction with magic immunity. For example, Time Lock deals magical damage with a physical stun. The stun will penetrate magic immunity but the damage will not. Headshot on the other hand deals physical damage with a magical stun; the damage will penetrate magic immunity but the stun will not.
nbsp;
Bashes that deal physical damage add their damage directly to a hero's physical attack, and will therefore grant lifesteal, and Cleave. Slardar's Bash, Faceless Void's Time Lock, Sniper's Headshot and Roshan's Bash are subject to pseudo-random distribution. If a new bash occurs before the old one finishes, the new one refreshes duration.

Sources of Bash

Abyssal Blade - Bash 6750 Chance: 25% melee / 10% ranged Duration: 1.4 Stun Type: Physical	Faceless Void - Time Lock Chance: 10/15/20/25% Damage: 40/50/60/70 Duration: 1 (2 on creeps) Damage Type: Magical Stun Type: Physical Average Damage Increase: 4/7.5/12/17.5 Deals twice as much damage when it procs on a target in Chronosphere.
Monkey King Bar - Mini-Bash 5400 Chance: 35% Damage: 100 Duration: 0.01 Damage Type: Magical Stun Type: Magical Average Damage Increase: 35	Roshan - Bash Chance: 15% Damage: 50 Duration: 1.65 Damage Type: Magical Stun Type: Physical Average Damage Increase: 7.5
Skull Basher - Bash 2950 Chance: 25% melee / 10% ranged Duration: 1.4 Stun Type: Physical	Slardar - Bash Chance: 10/15/20/25% Damage: 40/50/60/70 Duration: 1 (2 on creeps) Damage Type: Physical Stun Type: Physical Average Damage Increase: 4/7.5/12/17.5
Sniper - Headshot Chance: 40% Damage: 15/40/65/90 Duration: 0.25 Damage Type: Physical Stun Type: Magical Average Damage Increase: 6/16/26/36	Spirit Breaker - Greater Bash Chance: 17% Damage: 10/20/30/40% of Spirit Breaker's movement speed Duration: 1/1.2/1.4/1.6 Damage Type: Magical Stun Type: Physical Average Damage Increase: 1.7/3.4/5.1/6.8% of Spirit Breaker's movement speed
Troll Warlord - Berserker's Rage Chance: 10% Damage: 20/30/40/50 Duration: 0.8/1.2/1.6/2 Damage Type: Magical Stun Type: Physical Average Damage Increase: 2/3/4/5