Short answer. Your father's estate alone. Article 1072 of the Civil Code says a donation given by both parents is split, half to each inheritance, but what is given by one parent alone is brought to collation only in that parent's own inheritance. Since your father gave it alone, it is charged only to his own estate.
What the law says
In the collation of a donation made by both parents, one-half shall be brought to the inheritance of the father, and the other half, to that of the mother.
Civil Code, Article 1072 — Donations by Both Parents. Read the full provision →
What the law says
That given by one alone shall be brought to collation in his or her inheritance.
Civil Code, Article 1072 — Donations by Both Parents. Read the full provision →
Why the source of the gift matters at all
Collation exists to keep succession fair among the children who eventually inherit — a gift a parent made during life is later brought back into account so it does not unfairly favor the child who received it over siblings who did not. Article 1072 answers a practical question that follows from that purpose: when two parents are both alive and only one of them made the gift, whose eventual estate absorbs it.
The rule for a joint donation by both parents
Article 1072 first addresses what happens when both parents give the donation together. In the collation of a donation made by both parents, one-half shall be brought to the inheritance of the father, and the other half, to that of the mother. A jointly given donation is split evenly between the two parents' estates for collation purposes, regardless of which parent's property actually funded the gift.
The separate rule for a donation from just one parent
Article 1072 then states the rule that answers your question directly: That given by one alone shall be brought to collation in his or her inheritance. A gift your father gave alone, without your mother also being a donor, is collated entirely against your father's own inheritance, not divided between both parents' estates the way a joint gift would be.
Why it matters which parent actually gave the gift
The article ties the collation entirely to who actually made the donation. Since only your father gave the gift, the fifty-fifty split that applies to a joint donation from both parents does not apply here at all — the full value of what he gave is accounted for against his estate alone when his succession is eventually settled, not spread across both parents.
What this means for your mother's estate
Because Article 1072 charges a single parent's donation only to that parent's own inheritance, the gift your father gave has no bearing on collation in your mother's estate. When her succession is eventually settled, this particular donation is not part of what gets brought into account for her inheritance, since she was not the one who gave it, and the article does not attribute a father's gift to her in any proportion, whether large or small.