In the episode "One Minute" of Breaking Bad, Hank gets a phone call from a digitally modified voice, telling him that he would be killed in a minute's time. Who initiated this phone call?
Fairly sure it was mentioned on the show, but also according to AMC's character page for Gus, he's the one who tipped off Hank.
Meanwhile, two Cartel killers, the Cousins, travel from Mexico to murder Walt to avenge the death of Tuco, his previous distributor. Gus instead steers them toward DEA Agent Hank Schrader but also tips off Hank about the attack.
Gus was the one who warned Hank about the attack. It was also mentioned here, under the trivia section... http://breakingbad.wikia.com/wiki/One_Minute