Warning! Spoilers for Action Comics #1035 by DC Comics below
The friendship between Batman and Superman is one of the greatest in all comics, but that doesn't mean the pair always fully trust each other. In Action Comics #1035, Superman is booted from the Justice League after causing an international incident involving a powerful artifact called the Genesis Fragment. However, when Batman asks about its whereabouts, the Man of Steel doesn't tell his closest friend where it's been hidden.
Following the arrival of Kryptonian refugees on Earth, Superman's quest to save the rest of them on Mongul's Warworld has become his primary focus. He tried to help the refugees who touched down at his home, but Mongul's army killed all of them except for Thao-La. In doing so, Mongul destroyed the refugees' ship, which carried the powerful Genesis Fragment - sending it crashing into the ocean. A fight over the possession of the powerful alien artifact created conflict between the US Navy and Atlanteans, leading Superman to take it from the sea and hide it so that neither side could use the cube in the act of war.
In Action Comics #1035 by Philip Kennedy Johnson, Daniel Sampere, Adriano Lucas, and Dave Sharpe, the Justice League sees no other option but to kick Superman from the team for interfering in a tense international incident. Superman accepts the punishment, as he's entirely focused on heading to Warworld to stop Mongul and free those enslaved on the planet. However, before he departs, Batman asks him about the Genesis Fragment's location. Superman tells him he doesn't need to worry about it while adding his warning to the League not to look for it extends to him as well.
Superman knows Batman will likely subvert his wishes for the Justice League not to come looking for the Genesis Fragment and tells him not to seek it out. While Kal-El reassures Bruce Wayne that he will be fine after leaving for Warworld, he knows Batman will try to look for the cube in his absence. Superman also understands the limits of their friendship but appreciates the Dark Knight's warning about flying into a trap. It's a great character moment between the two DC heroes.
Being Batman's friend isn't the easiest thing to pull off, as the Gotham City hero will often look at things analytically, not emotionally. While his concern for Superman is genuine, as he's worried about his friend's safety, it doesn't stop him from seeking out the Genesis Fragment. Superman understands Batman won't relent in his quest but doesn't give him the information he desires. The two heroes will always trust each other, but both understand keeping some things secret from one another is necessary.