It has been some time since the Tournament of Power took place in Dragon Ball Super, but a particular scene that took place before the tournament finally proved Goku's true nature. While he is considered one of the most trustworthy characters in the franchise, evidently, Goku is willing to go to any extent to fulfill his mission.
The Tournament of Power was a battle created by Zeno upon Goku's request. While Goku had initially picked Majin Buu to be in Universe 7 team, he happened to sleep right before the tournament. This forced Goku to look for a new teammate and he happened to find one in his then-deceased enemy Frieza.
Dragon Ball Super: How did Goku lie to Frieza?
After the Tournament of Power was announced, Goku immediately began gathering teammates for the competition. While Majin Buu was one of the first names on Goku's list, when he went to invite him to the tournament, Buu was fast asleep. Given that he did not have enough time to wait for Buu to wake up, Goku had to look for a new teammate.
That's when he got the idea to invite Frieza to be part of the Universe 7 team. At the time Frieza was dead, however, Goku remembered how he was able to attend the Martial Arts Tournament when he had passed away years ago. Thus, similar to how he came back to life for a single day, Goku got similar permission for Frieza as well.
However, that was not enough as he needed to convince Frieza to fight with them. When Goku went to invite Frieza, he had to convince the galactic emperor to join their team by promising him that he would revive him back to life using the Earth's dragon balls after the tournament.
While it seemed like a bad plan to Goku's friends, it was a blatant lie. As Dragon Ball fans would know, the Earth's dragon balls can be used to revive a person only once. Given that Frieza had already been revived using the Earth's dragon balls during the Resurrection F storyline, Frieza can no longer be revived using the same.
While the Dragon Ball Super anime portrayed the scene in such a way that Goku was hiding something from Frieza, meaning that he knowingly lied to him, the same wasn't the case in the manga. When Goku made the promise to Frieza in the manga, it seemed very evident that Goku really intended to revive Frieza after the Tournament of Power.
Thus, when one looks at the scene in the Dragon Ball Super manga, it seems like Goku had completely forgotten about the dragon balls' rules or the fact that Frieza had already been revived once using the same. Nevertheless, given the fact that in the case of Dragon Ball Super, the anime came first, one can consider it to be the source material. This meant that Goku blatantly lied to Frieza in the hope of not fulfilling his promise after the tournament ended.