How to preserve the date column by exporting a ts or xts object from R to excel?

Question

I am working with a ts file with two variables

compib <- cbind(pimsaf, fumosaf)

head(compib)
      pimsaf  fumosaf
[1,] 77.74133 131.5189
[2,] 80.18227 131.6221
[3,] 79.77395 111.2698
[4,] 79.48862 117.7251
[5,] 79.19464 110.1054
[6,] 79.41282 105.1417

If I try directly in "write.xlsx" it does not consider the dates, if I try to turn into a dataframe it returns me distorted dates:

date   pimsaf  fumosaf
1 2002.000 77.74133 131.5189
2 2002.083 80.18227 131.6221
3 2002.167 79.77395 111.2698
4 2002.250 79.48862 117.7251
5 2002.333 79.19464 110.1054
6 2002.417 79.41282 105.1417

Is there any easier way to export ts directly to excel?