What is the ruling on walking forward to fill a gap in the row during Dhuhr prayer, and does the prayer become invalid by this movement?

The correct action is for the worshipper to advance and fill the gaps in the row in front of him. His prayer is not invalidated by taking a few steps for the purpose of filling a gap. It is stated in Al-Taj wal-Iklil by Al-Mawwaq Al-Maliki: "The matter in prayer is to fill the gaps. So, if he sees a gap while praying in front of him, or to his right, or to his left, and he finds a way to fill it, he should advance to it and fill it. There is no harm in him cutting through rows to reach it." The prayer is not invalidated according to some Hanafis by the worshipper walking to fill a gap, nor according to the Shafi'is by taking one or two steps. However, three consecutive steps or more invalidate the prayer.