Look it up. It was made with Russia.
Funny, but...
Seriously though... I've looked it up and it ain't in there.
It appears that it was offered as part of the negotiations for German Reunification in February 1990, and the assurances were quite strong at the time, but by May, 1990, Gorbachev apparently conceded,
"nations could choose which military alliances they would join”, in turn for an American promise to,
“seek to avoid doing anything that would damage [the USSR’s] position in the world.” By September, even that last assurance didn't make it into the final agreement.
So in the early days of the negotiation it was offered and how that offer would look was intently discussed, but as the negotiations dragged on, the Soviet Union was growing weaker in reality and thus at the negotiating table. The US realized they didn't need to offer the USSR such a wide concession and the deal turned more favorably to the United States/NATO interests.
The final deal that was agreed to did
not include a commitment to not expand NATO. By the time the treaty was ratified, the USSR wouldn't have been able to hold on to Germany anyways. There was nothing the West needed to concede to anyways. But there were some concessions...
-Germany could not have a nuclear arsenal of its own.
-Germany could not commit acts tending to and undertaken with the intent to disturb the peaceful relations between nations, especially to prepare for aggressive war.
-Germany would undertake to reduce the personnel strength of the armed forces of the united Germany to 370,000 (ground, air and naval forces) within three to four years.
-Among other things....
But no mention of NATO is made.
Here is the document for review:
Or perhaps I am looking at the wrong document? Is there another agreement that this promise applies to?